We’re fans of Custom Elements around here. Their design makes them particularly amenable to lazy loading, which can be a boon for performance.
Inspired by a colleague’s experiments, I recently set about writing a simple auto-loader: Whenever a custom element appears in the DOM, we wanna load the corresponding implementation if it’s not available yet. The browser then takes care of upgrading such elements from there on out.
Chances are you won’t actually need all this; there’s usually a simpler approach. Used deliberately, the techniques shown here might still be a useful addition to your toolset.
For consistency, we want our auto-loader to be a custom element as well — which also means we can easily configure it via HTML. But first, let’s identify those unresolved custom elements, step by step:
class AutoLoader extends HTMLElement {
connectedCallback() {
let scope = this.parentNode;
this.discover(scope);
}
}
customElements.define("ce-autoloader", AutoLoader);Assuming we’ve loaded this module up-front (using async is ideal), we can drop a <ce-autoloader> element into the <body> of our document. That will immediately start the discovery process for all child elements of <body>, which now constitutes our root element. We could limit discovery to a subtree of our document by adding <ce-autoloader> to the respective container element instead — indeed, we might even have multiple instances for different subtrees.
Of course, we still have to implement that discover method (as part of the AutoLoader class above):
discover(scope) {
let candidates = [scope, ...scope.querySelectorAll("*")];
for(let el of candidates) {
let tag = el.localName;
if(tag.includes("-") && !customElements.get(tag)) {
this.load(tag);
}
}
}Here we check our root element along with every single descendant (*). If it’s a custom element — as indicated by hyphenated tags — but not yet upgraded, we’ll attempt to load the corresponding definition. Querying the DOM that way might be expensive, so we should be a little careful. We can alleviate load on the main thread by deferring this work:
connectedCallback() {
let scope = this.parentNode;
requestIdleCallback(() => {
this.discover(scope);
});
}requestIdleCallback is not universally supported yet, but we can use requestAnimationFrame as a fallback:
let defer = window.requestIdleCallback || requestAnimationFrame;
class AutoLoader extends HTMLElement {
connectedCallback() {
let scope = this.parentNode;
defer(() => {
this.discover(scope);
});
}
// ...
}Now we can move on to implementing the missing load method to dynamically inject a <script> element:
load(tag) {
let el = document.createElement("script");
let res = new Promise((resolve, reject) => {
el.addEventListener("load", ev => {
resolve(null);
});
el.addEventListener("error", ev => {
reject(new Error("failed to locate custom-element definition"));
});
});
el.src = this.elementURL(tag);
document.head.appendChild(el);
return res;
}
elementURL(tag) {
return `${this.rootDir}/${tag}.js`;
}Note the hard-coded convention in elementURL. The src attribute’s URL assumes there’s a directory where all custom element definitions reside (e.g. <my-widget> → /components/my-widget.js). We could come up with more elaborate strategies, but this is good enough for our purposes. Relegating this URL to a separate method allows for project-specific subclassing when needed:
class FancyLoader extends AutoLoader {
elementURL(tag) {
// fancy logic
}
}Either way, note that we’re relying on this.rootDir. This is where the aforementioned configurability comes in. Let’s add a corresponding getter:
get rootDir() {
let uri = this.getAttribute("root-dir");
if(!uri) {
throw new Error("cannot auto-load custom elements: missing `root-dir`");
}
if(uri.endsWith("/")) { // remove trailing slash
return uri.substring(0, uri.length - 1);
}
return uri;
}You might be thinking of observedAttributes now, but that doesn’t really make things easier. Plus updating root-dir at runtime seems like something we’re never going to need.
Now we can — and must — configure our elements directory: <ce-autoloader root-dir="/components">.
With this, our auto-loader can do its job. Except it only works once, for elements that already exist when the auto-loader is initialized. We’ll probably want to account for dynamically added elements as well. That’s where MutationObserver comes into play:
connectedCallback() {
let scope = this.parentNode;
defer(() => {
this.discover(scope);
});
let observer = this._observer = new MutationObserver(mutations => {
for(let { addedNodes } of mutations) {
for(let node of addedNodes) {
defer(() => {
this.discover(node);
});
}
}
});
observer.observe(scope, { subtree: true, childList: true });
}
disconnectedCallback() {
this._observer.disconnect();
}This way, the browser notifies us whenever a new element appears in the DOM — or rather, our respective subtree — which we then use to restart the discovery process. (You might argue we’re re-inventing custom elements here, and you’d be kind of correct.)
Our auto-loader is now fully functional. Future enhancements might look into potential race conditions and investigate optimizations. But chances are this is good enough for most scenarios. Let me know in the comments if you have a different approach and we can compare notes!
An Approach to Lazy Loading Custom Elements originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
It’s a question I hear asked quite often: Is it possible to create shadows from gradients instead of solid colors? There is no specific CSS property that does this (believe me, I’ve looked) and any blog post you find about it is basically a lot of CSS tricks to approximate a gradient. We’ll actually cover some of those as we go.
But first… another article about gradient shadows? Really?
Yes, this is yet another post on the topic, but it is different. Together, we’re going to push the limits to get a solution that covers something I haven’t seen anywhere else: transparency. Most of the tricks work if the element has a non-transparent background but what if we have a transparent background? We will explore this case here!
Before we start, let me introduce my gradient shadows generator. All you have to do is to adjust the configuration, and get the code. But follow along because I’m going to help you understand all the logic behind the generated code.
Let’s start with the solution that’ll work for 80% of most cases. The most typical case: you are using an element with a background, and you need to add a gradient shadow to it. No transparency issues to consider there.
The solution is to rely on a pseudo-element where the gradient is defined. You place it behind the actual element and apply a blur filter to it.
.box {
position: relative;
}
.box::before {
content: "";
position: absolute;
inset: -5px; /* control the spread */
transform: translate(10px, 8px); /* control the offsets */
z-index: -1; /* place the element behind */
background: /* your gradient here */;
filter: blur(10px); /* control the blur */
}It looks like a lot of code, and that’s because it is. Here’s how we could have done it with a box-shadow instead if we were using a solid color instead of a gradient.
box-shadow: 10px 8px 10px 5px orange;That should give you a good idea of what the values in the first snippet are doing. We have X and Y offsets, the blur radius, and the spread distance. Note that we need a negative value for the spread distance that comes from the inset property.
Here’s a demo showing the gradient shadow next to a classic box-shadow:
If you look closely you will notice that both shadows are a little different, especially the blur part. It’s not a surprise because I am pretty sure the filter property’s algorithm works differently than the one for box-shadow. That’s not a big deal since the result is, in the end, quite similar.
This solution is good, but still has a few drawbacks related to the z-index: -1 declaration. Yes, there is “stacking context” happening there!
I applied a transform to the main element, and boom! The shadow is no longer below the element. This is not a bug but the logical result of a stacking context. Don’t worry, I will not start a boring explanation about stacking context (I already did that in a Stack Overflow thread), but I’ll still show you how to work around it.
The first solution that I recommend is to use a 3D transform:
.box {
position: relative;
transform-style: preserve-3d;
}
.box::before {
content: "";
position: absolute;
inset: -5px;
transform: translate3d(10px, 8px, -1px); /* (X, Y, Z) */
background: /* .. */;
filter: blur(10px);
}Instead of using z-index: -1, we will use a negative translation along the Z-axis. We will put everything inside translate3d(). Don’t forget to use transform-style: preserve-3d on the main element; otherwise, the 3D transform won’t take effect.
As far as I know, there is no side effect to this solution… but maybe you see one. If that’s the case, share it in the comment section, and let’s try to find a fix for it!
If for some reason you are unable to use a 3D transform, the other solution is to rely on two pseudo-elements — ::before and ::after. One creates the gradient shadow, and the other reproduces the main background (and other styles you might need). That way, we can easily control the stacking order of both pseudo-elements.
.box {
position: relative;
z-index: 0; /* We force a stacking context */
}
/* Creates the shadow */
.box::before {
content: "";
position: absolute;
z-index: -2;
inset: -5px;
transform: translate(10px, 8px);
background: /* .. */;
filter: blur(10px);
}
/* Reproduces the main element styles */
.box::after {
content: """;
position: absolute;
z-index: -1;
inset: 0;
/* Inherit all the decorations defined on the main element */
background: inherit;
border: inherit;
box-shadow: inherit;
}It’s important to note that we are forcing the main element to create a stacking context by declaring z-index: 0, or any other property that do the same, on it. Also, don’t forget that pseudo-elements consider the padding box of the main element as a reference. So, if the main element has a border, you need to take that into account when defining the pseudo-element styles. You will notice that I am using inset: -2px on ::after to account for the border defined on the main element.
As I said, this solution is probably good enough in a majority of cases where you want a gradient shadow, as long as you don’t need to support transparency. But we are here for the challenge and to push the limits, so even if you don’t need what is coming next, stay with me. You will probably learn new CSS tricks that you can use elsewhere.
Let’s pick up where we left off on the 3D transform and remove the background from the main element. I will start with a shadow that has both offsets and spread distance equal to 0.
The idea is to find a way to cut or hide everything inside the area of the element (inside the green border) while keeping what is outside. We are going to use clip-path for that. But you might wonder how clip-path can make a cut inside an element.
Indeed, there’s no way to do that, but we can simulate it using a particular polygon pattern:
clip-path: polygon(-100vmax -100vmax,100vmax -100vmax,100vmax 100vmax,-100vmax 100vmax,-100vmax -100vmax,0 0,0 100%,100% 100%,100% 0,0 0)Tada! We have a gradient shadow that supports transparency. All we did is add a clip-path to the previous code. Here is a figure to illustrate the polygon part.
The blue area is the visible part after applying the clip-path. I am only using the blue color to illustrate the concept, but in reality, we will only see the shadow inside that area. As you can see, we have four points defined with a big value (B). My big value is 100vmax, but it can be any big value you want. The idea is to ensure we have enough space for the shadow. We also have four points that are the corners of the pseudo-element.
The arrows illustrate the path that defines the polygon. We start from (-B, -B) until we reach (0,0). In total, we need 10 points. Not eight points because two points are repeated twice in the path ((-B,-B) and (0,0)).
There’s still one more thing left for us to do, and it’s to account for the spread distance and the offsets. The only reason the demo above works is because it is a particular case where the offsets and spread distance are equal to 0.
Let’s define the spread and see what happens. Remember that we use inset with a negative value to do this:
The pseudo-element is now bigger than the main element, so the clip-path cuts more than we need it to. Remember, we always need to cut the part inside the main element (the area inside the green border of the example). We need to adjust the position of the four points inside of clip-path.
.box {
--s: 10px; /* the spread */
position: relative;
}
.box::before {
inset: calc(-1 * var(--s));
clip-path: polygon(
-100vmax -100vmax,
100vmax -100vmax,
100vmax 100vmax,
-100vmax 100vmax,
-100vmax -100vmax,
calc(0px + var(--s)) calc(0px + var(--s)),
calc(0px + var(--s)) calc(100% - var(--s)),
calc(100% - var(--s)) calc(100% - var(--s)),
calc(100% - var(--s)) calc(0px + var(--s)),
calc(0px + var(--s)) calc(0px + var(--s))
);
}We’ve defined a CSS variable, --s, for the spread distance and updated the polygon points. I didn’t touch the points where I am using the big value. I only update the points that define the corners of the pseudo-element. I increase all the zero values by --s and decrease the 100% values by --s.
It’s the same logic with the offsets. When we translate the pseudo-element, the shadow is out of alignment, and we need to rectify the polygon again and move the points in the opposite direction.
.box {
--s: 10px; /* the spread */
--x: 10px; /* X offset */
--y: 8px; /* Y offset */
position: relative;
}
.box::before {
inset: calc(-1 * var(--s));
transform: translate3d(var(--x), var(--y), -1px);
clip-path: polygon(
-100vmax -100vmax,
100vmax -100vmax,
100vmax 100vmax,
-100vmax 100vmax,
-100vmax -100vmax,
calc(0px + var(--s) - var(--x)) calc(0px + var(--s) - var(--y)),
calc(0px + var(--s) - var(--x)) calc(100% - var(--s) - var(--y)),
calc(100% - var(--s) - var(--x)) calc(100% - var(--s) - var(--y)),
calc(100% - var(--s) - var(--x)) calc(0px + var(--s) - var(--y)),
calc(0px + var(--s) - var(--x)) calc(0px + var(--s) - var(--y))
);
}There are two more variables for the offsets: --x and --y. We use them inside of transform and we also update the clip-path values. We still don’t touch the polygon points with big values, but we offset all the others — we reduce --x from the X coordinates, and --y from the Y coordinates.
Now all we have to do is to update a few variables to control the gradient shadow. And while we are at it, let’s also make the blur radius a variable as well:
Do we still need the 3D
transformtrick?
It all depends on the border. Don’t forget that the reference for a pseudo-element is the padding box, so if you apply a border to your main element, you will have an overlap. You either keep the 3D transform trick or update the inset value to account for the border.
Here is the previous demo with an updated inset value in place of the 3D transform:
I‘d say this is a more suitable way to go because the spread distance will be more accurate, as it starts from the border-box instead of the padding-box. But you will need to adjust the inset value according to the main element’s border. Sometimes, the border of the element is unknown and you have to use the previous solution.
With the earlier non-transparent solution, it’s possible you will face a stacking context issue. And with the transparent solution, it’s possible you face a border issue instead. Now you have options and ways to work around those issues. The 3D transform trick is my favorite solution because it fixes all the issues (The online generator will consider it as well)
If you try adding border-radius to the element when using the non-transparent solution we started with, it is a fairly trivial task. All you need to do is to inherit the same value from the main element, and you are done.
Even if you don’t have a border radius, it’s a good idea to define border-radius: inherit. That accounts for any potential border-radius you might want to add later or a border radius that comes from somewhere else.
It’s a different story when dealing with the transparent solution. Unfortunately, it means finding another solution because clip-path cannot deal with curvatures. That means we won’t be able to cut the area inside the main element.
We will introduce the mask property to the mix.
This part was very tedious, and I struggled to find a general solution that doesn’t rely on magic numbers. I ended up with a very complex solution that uses only one pseudo-element, but the code was a lump of spaghetti that covers only a few particular cases. I don’t think it is worth exploring that route.
I decided to insert an extra element for the sake of simpler code. Here’s the markup:
<div class="box">
<sh></sh>
</div>I am using a custom element, <sh>, to avoid any potential conflict with external CSS. I could have used a <div>, but since it’s a common element, it can easily be targeted by another CSS rule coming from somewhere else that can break our code.
The first step is to position the <sh> element and purposely create an overflow:
.box {
--r: 50px;
position: relative;
border-radius: var(--r);
}
.box sh {
position: absolute;
inset: -150px;
border: 150px solid #0000;
border-radius: calc(150px + var(--r));
}The code may look a bit strange, but we’ll get to the logic behind it as we go. Next, we create the gradient shadow using a pseudo-element of <sh>.
.box {
--r: 50px;
position: relative;
border-radius: var(--r);
transform-style: preserve-3d;
}
.box sh {
position: absolute;
inset: -150px;
border: 150px solid #0000;
border-radius: calc(150px + var(--r));
transform: translateZ(-1px)
}
.box sh::before {
content: "";
position: absolute;
inset: -5px;
border-radius: var(--r);
background: /* Your gradient */;
filter: blur(10px);
transform: translate(10px,8px);
}As you can see, the pseudo-element uses the same code as all the previous examples. The only difference is the 3D transform defined on the <sh> element instead of the pseudo-element. For the moment, we have a gradient shadow without the transparency feature:
Note that the area of the <sh> element is defined with the black outline. Why I am doing this? Because that way, I am able to apply a mask on it to hide the part inside the green area and keep the overflowing part where we need to see the shadow.
I know it’s a bit tricky, but unlike clip-path, the mask property doesn’t account for the area outside an element to show and hide things. That’s why I was obligated to introduce the extra element — to simulate the “outside” area.
Also, note that I am using a combination of border and inset to define that area. This allows me to keep the padding-box of that extra element the same as the main element so that the pseudo-element won’t need additional calculations.
Another useful thing we get from using an extra element is that the element is fixed, and only the pseudo-element is moving (using translate). This will allow me to easily define the mask, which is the last step of this trick.
mask:
linear-gradient(#000 0 0) content-box,
linear-gradient(#000 0 0);
mask-composite: exclude;It’s done! We have our gradient shadow, and it supports border-radius! You probably expected a complex mask value with oodles of gradients, but no! We only need two simple gradients and a mask-composite to complete the magic.
Let’s isolate the <sh> element to understand what is happening there:
.box sh {
position: absolute;
inset: -150px;
border: 150px solid red;
background: lightblue;
border-radius: calc(150px + var(--r));
}Here’s what we get:
Note how the inner radius matches the main element’s border-radius. I have defined a big border (150px) and a border-radius equal to the big border plus the main element’s radius. On the outside, I have a radius equal to 150px + R. On the inside, I have 150px + R - 150px = R.
We must hide the inner (blue) part and make sure the border (red) part is still visible. To do that, I’ve defined two mask layers —One that covers only the content-box area and another that covers the border-box area (the default value). Then I excluded one from another to reveal the border.
mask:
linear-gradient(#000 0 0) content-box,
linear-gradient(#000 0 0);
mask-composite: exclude;I used the same technique to create a border that supports gradients and border-radius. Ana Tudor has also a good article about masking composite that I invite you to read.
Are there any drawbacks to this method?
Yes, this definitely not perfect. The first issue you may face is related to using a border on the main element. This may create a small misalignment in the radii if you don’t account for it. We have this issue in our example, but perhaps you can hardly notice it.
The fix is relatively easy: Add the border’s width for the <sh> element’s inset.
.box {
--r: 50px;
border-radius: var(--r);
border: 2px solid;
}
.box sh {
position: absolute;
inset: -152px; /* 150px + 2px */
border: 150px solid #0000;
border-radius: calc(150px + var(--r));
}Another drawback is the big value we’re using for the border (150px in the example). This value should be big enough to contain the shadow but not too big to avoid overflow and scrollbar issues. Luckily, the online generator will calculate the optimal value considering all the parameters.
The last drawback I am aware of is when you’re working with a complex border-radius. For example, if you want a different radius applied to each corner, you must define a variable for each side. It’s not really a drawback, I suppose, but it can make your code a bit tougher to maintain.
.box {
--r-top: 10px;
--r-right: 40px;
--r-bottom: 30px;
--r-left: 20px;
border-radius: var(--r-top) var(--r-right) var(--r-bottom) var(--r-left);
}
.box sh {
border-radius: calc(150px + var(--r-top)) calc(150px + var(--r-right)) calc(150px + var(--r-bottom)) calc(150px + var(--r-left));
}
.box sh:before {
border-radius: var(--r-top) var(--r-right) var(--r-bottom) var(--r-left);
}The online generator only considers a uniform radius for the sake of simplicity, but you now know how to modify the code if you want to consider a complex radius configuration.
We’ve reached the end! The magic behind gradient shadows is no longer a mystery. I tried to cover all the possibilities and any possible issues you might face. If I missed something or you discover any issue, please feel free to report it in the comment section, and I’ll check it out.
Again, a lot of this is likely overkill considering that the de facto solution will cover most of your use cases. Nevertheless, it’s good to know the “why” and “how” behind the trick, and how to overcome its limitations. Plus, we got good exercise playing with CSS clipping and masking.
And, of course, you have the online generator you can reach for anytime you want to avoid the hassle.
Different Ways to Get CSS Gradient Shadows originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
Every now and then, a one blog post is published and it spurs a reaction or response in others that are, in turn, published as blogs posts, and a theme starts to emerge. That’s what happened this past week and the theme developed around the cost of JavaScript frameworks — a cost that, in this case, reveals just how darn important it is to use JavaScript responsibly.
This is where the story begins. Eric goes to a health service provider website to book an appointment and gets… a blank screen.
In addition to a terrifying amount of telemetry, Modern Health’s customer-facing experience is delivered using React and Webpack.
If you are familiar with how the web is built, what happened is pretty obvious: A website that over-relies on JavaScript to power its experience had its logic collide with one or more other errant pieces of logic that it summons. This created a deadlock.
If you do not make digital experiences for a living, what happened is not obvious at all. All you see is a tiny fake loading spinner that never stops.
D’oh. This might be mere nuisance — or even laughable — in some situations, but not when someone’s health is on the line:
A person seeking help in a time of crisis does not care about TypeScript, tree shaking, hot module replacement, A/B tests, burndown charts, NPS, OKRs, KPIs, or other startup jargon. Developer experience does not count for shit if the person using the thing they built can’t actually get what they need.
This is the big smack of reality. What happens when our tooling and reporting — the very things that are supposed to make our work more effective — get in the way of the user experience? These are tools that provide insights that can help us anticipate a user’s needs, especially in a time of need.
I realize that pointing the finger at JavaScript frameworks is already divisive. But this goes beyond whether you use React or framework d’jour. It’s about business priorities and developer experience conflicting with user experiences.
Partisans for slow, complex frameworks have successfully marketed lemons as the hot new thing, despite the pervasive failures in their wake, crowding out higher-quality options in the process.
These technologies were initially pitched on the back of “better user experiences”, but have utterly failed to deliver on that promise outside of the high-management-maturity organisations in which they were born. Transplanted into the wider web, these new stacks have proven to be expensive duds.
There’s the rub. Alex ain’t mincing words, but notice that the onus is on the way frameworks haved been marketed to developers than developers themselves. The sales pitch?
Once the lemon sellers embed the data-light idea that improved “Developer Experience” (“DX”) leads to better user outcomes, improving “DX” became and end unto itself, and many who knew better felt forced to play along. The long lead times in falsifying trickle-down UX was a feature, not a bug; they don’t need you to succeed, only to keep buying.
As marketing goes, the “DX” bait-and-switch is brilliant, but the tech isn’t delivering for anyone but developers.
Tough to stomach, right? No one wants to be duped, and it’s tough to admit a sunken cost when there is one. It gets downright personal if you’ve invested time in a specific piece of tech and effort integrating it into your stack. Development workflows are hard and settling into one is sorta like settling into a house you plan on living in a little while. But you’d want to know if your house was built on what Alex calls a “sandy foundation”.
I’d just like to pause here a moment to say I have no skin in this debate. As a web generalist, I tend to adopt new tools early for familiarity then drop them fast, relegating them to my toolshed until I find a good use for them. In other words, my knowledge is wide but not very deep in one area or thing. HTML, CSS, and JavaScript is my go-to cocktail, but I do care a great deal about user experience and know when to reach for a tool to solve a particular thing.
And let’s acknowledge that not everyone has a say in the matter. Many of us work on managed teams that are prescribed the tools we use. Alex says as much, which I think is important to call out because it’s clear this isn’t meant to be personal. It’s a statement on our priorities and making sure they along to user expectations.
Let’s alow Chris to steer us back to the story…
So, maybe your app is built on React and it doesn’t matter why it’s that way. There’s still work to do to ensure the app is reliable and accessible.
Just blocking a file shouldn’t totally wreck a website, but it often does! In JavaScript, that may be because the developers have written first-party JavaScript (which I’ll generally allow) that depends on third-party JavaScript (which I’ll generally block).
[…]
If I block resources from
tracking-website.com, now my first-party JavaScript is going to throw an error. JavaScript isn’t chill. If an error is thrown, it doesn’t execute more JavaScript further down in the file. If further down in that file istransitionToOnboarding();— that ain’t gonna work.
Maybe it’s worth revisiting your workflow and tweaking it to account to identify more points of failure.
So here’s an idea: Run your end-to-end tests in browsers that have popular content blockers with default configs installed.
Doing so may uncover problems like this that stop your customers, and indeed people in need, from being stopped in their tracks.
Good idea! Hey, anything that helps paint a more realistic picture of how the app is used. That sort of clarity could happen a lot earlier in the process, perhaps before settling on development decisions. Know your users. Why are they using the app? How do they browse the web? Where are they phsically located? What problems could get in their way? Chris has a great talk on that, too.
Healthcare, Selling Lemons, and the Price of Developer Experience originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
We often think of background images as texture or something that provides contrast for legible content — in other words, not really content. If it was content, you’d probably reach for an <img> anyway, accessibility and whatnot.
But there are times when the position or scale of a background image might sit somewhere between the poles of content and decoration. Context is king, right? If we change the background image’s position, it may convey a bit more context or experience.
How so? Let’s look at a few examples I’ve seen floating around.
As we get started, I’ll caution that there’s a fine line in these demos between images used for decoration and images used as content. The difference has accessibility implications where backgrounds are not announced to screen readers. If your image is really an image, then maybe consider an <img> tag with proper alt text. And while we’re talking accessibility, it’s a good idea to consider a user’s motion preference’s as well.
Chris Coyier has this neat little demo from several years back.
The demo is super practical in lots of ways because it’s a neat approach for displaying ads in content. You have the sales pitch and an enticing image to supplement it.
The big limitation for most ads, I’d wager, is the limited real estate. I don’t know if you’ve ever had to drop an ad onto a page, but I have and typically ask the advertiser for an image that meets exact pixel dimensions, so the asset fits the space.
But Chris’s demo alleviates the space issue. Hover the image and watch it both move and scale. The user actually gets more context for the product than they would have when the image was in its original position. That’s a win-win, right? The advertiser gets to create an eye-catching image without compromising context. Meanwhile, the user gets a little extra value from the newly revealed portions of the image.
If you peek at the demo’s markup, you’ll notice it’s pretty much what you’d expect. Here’s an abridged version:
<div class="ad-container">
<a href="#" target="_blank" rel="noopener">
<!-- Background image container -->
<div class="ad-image"></div>
</a>
<div class="ad-content">
<!-- Content -->
</div>
</div>We could probably quibble over the semantics a bit, but that’s not the point. We have a container with a linked-up <div> for the background image and another <div> to hold the content.
As far as styling goes, the important pieces are here:
.container {
background-image: url("/path/to/some/image.png");
background-repeat: no-repeat;
background-position: 0 0;
height: 400px;
width: 350px;
}Not bad, right? We give the container some dimensions and set a background image on it that doesn’t repeat and is positioned by its bottom-left edge.
The real trick is with JavaScript. We will use that to get the mouse position and the container’s offset, then convert that value to an appropriate scale to set the background-position. First, let’s listen for mouse movements on the .container element:
let container = document.querySelector(".container");
container.addEventListener("mousemove", function(e) {
// Our function
}
);From here, we can use the container’s offsetX and offsetY properties. But we won’t use these values directly, as the value for the X coordinate is smaller than what we need, and the Y coordinate is larger. We will have to play around a bit to find a constant that we can use as a multiplier.
It’s a bit touch-and-feel, but I’ve found that 1.32 and 0.455 work perfectly for the X and Y coordinates, respectively. We multiply the offsets by those values, append a px unit on the result, then apply it to the background-position values.
let container = document.querySelector(".container");
container.addEventListener("mousemove", function(e) {
container.style.backgroundPositionX = -e.offsetX * 1.32 + "px";
container.style.backgroundPositionY = -e.offsetY * 0.455 + "px";
}
);Lastly, we can also reset the background positions back to the original if the user leaves the image container.
container.addEventListener("mouseleave", function() {
container.style.backgroundPosition = "0px 0px";
}
);Since we’re on CSS-Tricks, I’ll offer that we could have done a much cheaper version of this with a little hover transition in vanilla CSS:
No doubt you’ve been to some online clothing store or whatever and encountered the ol’ zoom-on-hover feature.
This pattern has been around for what feels like forever (Dylan Winn-Brown shared his approach back in 2016), but that’s just a testament (I hope) to its usefulness. The user gets more context as they zoom in and get a better idea of a sweater’s stitching or what have you.
There’s two pieces to this: the container and the magnifier. The container is the only thing we need in the markup, as we’ll inject the magnifier element during the user’s interaction. So, behold our HTML!
<div class="container"></div>In the CSS, we will create width and height variables to store the dimensions of the of the magnifier glass itself. Then we’ll give that .container some shape and a background-image:
:root {
--magnifer-width: 85;
--magnifer-height: 85;
}
.container {
width: 500px;
height: 400px;
background-size: cover;
background-image: url("/path/to/image.png");
background-repeat: no-repeat;
position: relative;
}There are some things we already know about the magnifier before we even see it, and we can define those styles up-front, specifically the previously defined variables for the .maginifier‘s width and height:
.magnifier {
position: absolute;
width: calc(var(--magnifer-width) * 1px);
height: calc(var(--magnifer-height) * 1px);
border: 3px solid #000;
cursor: none;
background-image: url("/path/to/image.png");
background-repeat: no-repeat;
}It’s an absolutely-positioned little square that uses the same background image file as the .container. Do note that the calc function is solely used here to convert the unit-less value in the variable to pixels. Feel free to arrange that however you see fit as far as eliminating repetition in your code.
Now, let’s turn to the JavaScript that pulls this all together. First we need to access the CSS variable defined earlier. We will use this in multiple places later on. Then we need get the mouse position within the container because that’s the value we’ll use for the the magnifier’s background position.
// Get the css variables
let root = window.getComputedStyle(document.documentElement);
let magnifier_width = root.getPropertyValue("--magnifer-width");
let magnifier_height = root.getPropertyValue("--magnifer-height");
let container = document.querySelector(".container");
let rect = container.getBoundingClientRect();
let x = (e.pageX - rect.left);
let y = (e.pageY - rect.top);
// Take page scrolling into account
x = x - window.pageXOffset;
y = y - window.pageYOffset;What we need is basically a mousemove event listener on the .container. Then, we will use the event.pageX or event.pageY property to get the X or Y coordinate of the mouse. But to get the exact relative position of the mouse on an element, we need to subtract the position of the parent element from the mouse position we get from the JavaScript above. A “simple” way to do this is to use getBoundingClientRect(), which returns the size of an element and its position relative to the viewport.
Notice how I’m taking scrolling into account. If there is overflow, subtracting the window pageX and pageY offsets will ensure the effect runs as expected.
We will first create the magnifier div. Next, we will create a mousemove function and add it to the image container. In this function, we will give the magnifier a class attribute. We will also calculate the mouse position and give the magnifier the left and top values we calculated earlier.
Let’s go ahead and build the magnifier when we hear a mousemove event on the .container:
// create the magnifier
let magnifier = document.createElement("div");
container.append(magnifier);Now we need to make sure it has a class name we can scope to the CSS:
// run the function on `mousemove`
container.addEventListener("mousemove", (e) => {
magnifier.setAttribute("class", "magnifier");
}The example video I showed earlier positions the magnifier outside of the container. We’re gonna keep this simple and overlay it on top of the container instead as the mouse moves. We will use if statements to set the magnifier’s position only if the X and Y values are greater or equal to zero, and less than the container’s width or height. That should keep it in bounds. Just be sure to subtract the width and height of the magnifier from the X and Y values.
// Run the function on mouse move.
container.addEventListener("mousemove", (e) => {
magnifier.setAttribute("class", "magnifier");
// Get mouse position
let rect = container.getBoundingClientRect();
let x = (e.pageX - rect.left);
let y = (e.pageY - rect.top);
// Take page scrolling into account
x = x - window.pageXOffset;
y = y - window.pageYOffset;
// Prevent magnifier from exiting the container
// Then set top and left values of magnifier
if (x >= 0 && x <= container.clientWidth - magnifier_width) {
magnifier.style.left = x + "px";
}
if (y >= 0 && y <= container.clientHeight - magnifier_height) {
magnifier.style.top = y + "px";
}
});Last, but certainly not least… we need to play with the magnifier’s background image a bit. The whole point is that the user gets a BIGGER view of the background image based on where the hover is taking place. So, let’s define a magnifier we can use to scale things up. Then we’ll define variables for the background image’s width and height so we have something to base that scale on, and set all of those values on the .magnifier styles:
// Magnifier image configurations
let magnify = 2;
let imgWidth = 500;
let imgHeight = 400;
magnifier.style.backgroundSize = imgWidth * magnify + "px " + imgHeight * magnify + "px";Let’s take the X and Y coordinates of the magnifier’s image and apply them to the .magnifier element’s background-position. As before with the magnifier position, we need to subtract the width and height of the magnifier from the X and Y values using the CSS variables.
// the x and y positions of the magnifier image
let magnify_x = x * magnify + 15;
let magnify_y = y * magnify + 15;
// set backgroundPosition for magnifier if it is within image
if (
x <= container.clientWidth - magnifier_width &&
y <= container.clientHeight - magnifier_height
) {
magnifier.style.backgroundPosition = -magnify_x + "px " + -magnify_y + "px";
}Tada!
Have you seen the Ken Burns effect? It’s classic and timeless thing where an image is bigger than the container it’s in, then sorta slides and scales slow as a slug. Just about every documentary film in the world seems to use it for image stills. If you have an Apple TV, then you’ve certainly seen it on the screen saver.
There are plenty of examples over at CodePen if you wanna get a better idea.
You’ll see that there are a number of ways to approach this. Some use JavaScript. Others are 100% CSS. I’m sure the JavaScript approaches are good for some uses cases, but if the goal is simply to subtly scale the image, CSS is perfectly suitable.
We could spice things up a bit using multiple backgrounds rather than one. Or, better yet, if we expand the rules to use elements instead of background images, we can apply the same animation to all of the backgrounds and use a dash of animation-delay to stagger the effect.
Lots of ways to do this, of course! It can certainly be optimized with Sass and/or CSS variables. Heck, maybe you can pull it off with a single <div> If so, share it in the comments!
I don’t know if anything is cooler than Sarah Drasner’s “Happy Halloween” pen… and that’s from 2016! It is a great example that layers backgrounds and moves them at varying speeds to create an almost cinematic experience. Good gosh is that cool!
GSAP is the main driver there, but I imagine we could make a boiled-down version that simply translates each background layer from left to right at different speeds. Not as cool, of course, but certainly the baseline experience. Gotta make sure the start and end of each background image is consistent so it repeats seamlessly when the animation repeats.
That’s it for now! Pretty neat that we can use backgrounds for much more than texture and contrast. I’m absolutely positive there are tons of other clever interactions we can apply to backgrounds. Temani Afif did exactly that with a bunch of neat hover effects for links. What do you have in mind? Share it with me in the comments!
Moving Backgrounds originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
Geez, leave it to Patrick Brosset to talk CSS performance in the most approachable and practical way possible. Not that CSS is always what’s gunking up the speed, or even the lowest hanging fruit when it comes to improving performance.
But if you’re looking for gains on the CSS side of things, Patrick has a nice way of sniffing out your most expensive selectors using Edge DevTools:
From here, click on one of the Recalculated Style events in the Main waterfall view and you’ll get a new “Selector Stats” tab. Look at all that gooey goodness!
Now you see all of the selectors that were processed and they can be sorted by how long they took, how many times they matched, the number of matching attempts, and something called “fast reject count” which I learned is the number of elements that were easy and quick to eliminate from matching.
A lot of insights here if CSS is really the bottleneck that needs investigating. But read Patrick’s full post over on the Microsoft Edge Blog because he goes much deeper into the why’s and how’s, and walks through an entire case study.
To Shared Link — Permalink on CSS-Tricks
The truth about CSS selector performance originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
I used to have this boss who loved, loved, loved, loved to emphasize words. This was way back before we used a WYSIWYG editors and I’d have to handcode that crap.
<p>
I used to have this boss who <em>loved</em>, <strong>loved</strong>,
<strong><em>loved</em></strong>, <strong><em><u>loved</u></em></strong>
to emphasize words.
</p>(Let’s not go into the colors he used for even MOAR emphasis.)
Writing all that markup never felt great. The effort it took, sure, whatever. But is it even a good idea to add overload content with double — or more! — emphases?
For starters, the <strong> and <em> tags are designed for different uses. We got them back in HTML5, where:
<strong>: Is used to convey “strong importance, seriousness, or urgency for its contents”.<em>: Represents “stress emphasis”.So, <strong> gives the content more weight in the sense it suggests that the content in it is important or urgent. Think of a warning:
Warning: The following content has been flagged for being awesome.
It might be tempting to reach for <em> to do the same thing. Italicized text can be attention-grabbing after all. But it’s really meant as a hint to use more emphasis when readingt the content in it. For example, here are two versions of the same sentence with the emphasis in different locations:
<p>I ate the <em>entire</em> plate of burritos.</p>
<p>I ate the entire <em>plate</em> of burritos.</p>Both examples stress emphasis, but on different words. And they would sound different if you were to read them out loud. That makes <em> a great way to express tone in your writing. It changes the meaning of the sentence in a way that <strong> does not.
Those are two things you gotta weigh when emphasizing content. Like, there are plenty of instances where you may need to italicize content without affecting the meaning of the sentence. But those can be handled with other tags that render italics:
<i>: This is the classic one! Before HTML5, this was used to stress emphasis with italics all over the place. Now, it’s purely used to italicize content visually without changing the semantic meaning.<cite>: Indicating the source of a fact or figure. (“Source: CSS-Tricks“)<address>: Used to mark up contact information, not only physical addresses, but things like email addresses and phone numbers too. (
howdy@example.com
)It’s going to he the same thing with <strong>. Rather than using it for styling text you want to look heavier, it’s a better idea to use the classic <b> tag for boldfacing to avoid giving extra signficance to content that doesn’t need it. And remember, some elements like headings are already rendered in bold, thanks to the browser’s default styles. There’s no need to add even more strong emphasis.
There are legitimate cases where you may need to italicize part of a line that’s already emphasized. Or maybe add emphasis to a bit of text that’s already italicized.
A blockquote might be a good example. I’ve seen plenty of times where they are italicized for style, even though default browser styles don’t do it:
blockquote {
font-style: italic;
}What if we need to mention a movie title in that blockquote? That should be italicized. There’s no stress emphasis needed, so an <i> tag will do. But it’s still weird to italicize something when it’s already rendered that way:
<blockquote>
This movie’s opening weekend performance offers some insight in
to its box office momentum as it fights to justify its enormous
budget. In its first weekend, <i>Avatar: The Way of Water</i> made
$134 million in North America alone and $435 million globally.
</blockquote>In a situation where we’re italicizing something within italicized content like this, we’re supposed to remove the italics from the nested element… <i> in this case.
blockquote i {
font-style: normal;
}Container style queries will be super useful to nab all these instances if we get them:
blockquote {
container-name: quote;
font-style: italic;
}
@container quote (font-style: italic) {
em, i, cite, address {
font-style: normal;
}
}This little snippet evaluates the blockquote to see if it’s font-style is set to italic. If it is, then it’ll make sure the <em>, <i>, <cite>, and <address> elements are rendered as normal text, while retaining the semantic meaning if there is one.
I wouldn’t nest <strong> inside <em> like this:
<p>I ate the <em><strong>entire</strong></em> plate of burritos.</p>…or nest <em> inside <strong> instead:
<p>I ate the <em><strong>entire</strong></em> plate of burritos.</p>The rendering is fine! And it doesn’t matter what order they’re in… at least in modern browsers. Jennifer Kyrnin mentions that some browsers only render the tag nearest to the text, but I didn’t bump into that anywhere in my limited tests. But something to watch for!
The reason I wouldn’t nest one form of emphasis in another is because it simply isn’t needed. There is no grammar rule that calls for it. Like exclamation points, one form of emphasis is enough, and you ought to use the one that matches what you’re after whether it’s visual, weight, or announced emphasis.
And even though some screen readers are capable of announcing emphasized content, they won’t read the markup with any additional importance or emphasis. So, no additional accessibility perks either, as far as I can tell.
If you’re in the position where your boss is like mine and wants ALL the emphasis, I’d reach for the right HTML tag for the type of emphasis, then apply the rest of the styles with a mix of tags that don’t affect semantics with CSS to help account for anything browser styles won’t handle.
<style>
/* If `em` contains `b` or `u` tags */
em:has(b, u) {
color: #f8a100;
}
</style>
<p>
I used to have this boss who <em>loved</em>, <strong>loved</strong>,
<strong><em>loved</em></strong>, <strong><em><u>loved</u></em></strong>
to emphasize words.
</p>I might even do it with the <strong> tag too as a defensive measure:
/* If `em` contains `b` or `u` tags */
em:has(b, u),
/* If `strong` contains `em` or `u` tags */
strong:has(i, u) {
color: #f8a100;
}As long as we’re playing defense, we can identify errors where emphases are nested within emphases by highlighting them in red or something:
/* Highlight semantic emphases within semantic emphases */
em:has(strong),
strong:has(em) {
background: hsl(0deg 50% 50% / .25);
border: 1px dashed hsl(0deg 50% 50% / .25);
}Then I’d probably use that snippet from the last section that removes the default italic styling from an element when it is nested in another italiczed element.
Mayyyyybe:
<strong> in <em> or the other way around, there may be a browser or several that will.The Double Emphasis Thing originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
Do you know that kind of effect where someone’s head is poking through a circle or hole? The famous Porky Pig animation where he waves goodbye while popping out of a series of red rings is the perfect example, and Kilian Valkhof actually re-created that here on CSS-Tricks a while back.
I have a similar idea but tackled a different way and with a sprinkle of animation. I think it’s pretty practical and makes for a neat hover effect you can use on something like your own avatar.
See that? We’re going to make a scaling animation where the avatar seems to pop right out of the circle it’s in. Cool, right? Don’t look at the code and let’s build this animation together step-by-step.
If you haven’t checked the code of the demo and you are wondering how many divs this’ll take, then stop right there, because our markup is nothing but a single image element:
<img src="" alt="">Yes, a single element! The challenging part of this exercise is using the smallest amount of code possible. If you have been following me for a while, you should be used to this. I try hard to find CSS solutions that can be achieved with the smallest, most maintainable code possible.
I wrote a series of articles here on CSS-Tricks where I explore different hover effects using the same HTML markup containing a single element. I go into detail on gradients, masking, clipping, outlines, and even layout techniques. I highly recommend checking those out because I will re-use many of the tricks in this post.
An image file that’s square with a transparent background will work best for what we’re doing. Here’s the one I’m using if you want start with that.
I’m hoping to see lots of examples of this as possible using real images — so please share your final result in the comments when you’re done so we can build a collection!
Before jumping into CSS, let’s first dissect the effect. The image gets bigger on hover, so we’ll for sure use transform: scale() in there. There’s a circle behind the avatar, and a radial gradient should do the trick. Finally, we need a way to create a border at the bottom of the circle that creates the appearance of the avatar behind the circle.
Let’s get to work!
Let’s start by adding the transform:
img {
width: 280px;
aspect-ratio: 1;
cursor: pointer;
transition: .5s;
}
img:hover {
transform: scale(1.35);
}Nothing complicated yet, right? Let’s move on.
We said that the background would be a radial gradient. That’s perfect because we can create hard stops between the colors of a radial gradient, which make it look like we’re drawing a circle with solid lines.
img {
--b: 5px; /* border width */
width: 280px;
aspect-ratio: 1;
background:
radial-gradient(
circle closest-side,
#ECD078 calc(99% - var(--b)),
#C02942 calc(100% - var(--b)) 99%,
#0000
);
cursor: pointer;
transition: .5s;
}
img:hover {
transform: scale(1.35);
}Note the CSS variable, --b, I’m using there. It represents the thickness of the “border” which is really just being used to define the hard color stops for the red part of the radial gradient.
The next step is to play with the gradient size on hover. The circle needs to keep its size as the image grows. Since we are applying a scale() transformation, we actually need to decrease the size of the circle because it otherwise scales up with the avatar. So, while the image scales up, we need the gradient to scale down.
Let’s start by defining a CSS variable, --f, that defines the “scale factor”, and use it to set the size of the circle. I’m using 1 as the default value, as in that’s the initial scale for the image and the circle that we transform from.
Here is a demo to illustrate the trick. Hover to see what is happening behind the scenes:
I added a third color to the radial-gradient to better identify the area of the gradient on hover:
radial-gradient(
circle closest-side,
#ECD078 calc(99% - var(--b)),
#C02942 calc(100% - var(--b)) 99%,
lightblue
);Now we have to position our background at the center of the circle and make sure it takes up the full height. I like to declare everything directly on the background shorthand property, so we can add our background positioning and make sure it doesn’t repeat by tacking on those values right after the radial-gradient():
background: radial-gradient() 50% / calc(100% / var(--f)) 100% no-repeat;The background is placed at the center (50%), has a width equal to calc(100%/var(--f)), and has a height equal to 100%.
Nothing scales when --f is equal to 1 — again, our initial scale. Meanwhile, the gradient takes up the full width of the container. When we increase --f, the element’s size grows — thanks to the scale() transform — and the gradient’s size decreases.
Here’s what we get when we apply all of this to our demo:
We’re getting closer! We have the overflow effect at the top, but we still need to hide the bottom part of the image, so it looks like it is popping out of the circle rather than sitting in front of it. That’s the tricky part of this whole thing and is what we’re going to do next.
I first tried tackling this with the border-bottom property, but I was unable to find a way to match the size of the border to the size to the circle. Here’s the best I could get and you can immediately see it’s wrong:
The actual solution is to use the outline property. Yes, outline, not border. In a previous article, I show how outline is powerful and allows us to create cool hover effects. Combined with outline-offset, we have exactly what we need for our effect.
The idea is to set an outline on the image and adjust its offset to create the bottom border. The offset will depend on the scaling factor the same way the gradient size did.
Now we have our bottom “border” (actually an outline) combined with the “border” created by the gradient to create a full circle. We still need to hide portions of the outline (from the top and the sides), which we’ll get to in a moment.
Here’s our code so far, including a couple more CSS variables you can use to configure the image size (--s) and the “border” color (--c):
img {
--s: 280px; /* image size */
--b: 5px; /* border thickness */
--c: #C02942; /* border color */
--f: 1; /* initial scale */
width: var(--s);
aspect-ratio: 1;
cursor: pointer;
border-radius: 0 0 999px 999px;
outline: var(--b) solid var(--c);
outline-offset: calc((1 / var(--f) - 1) * var(--s) / 2 - var(--b));
background:
radial-gradient(
circle closest-side,
#ECD078 calc(99% - var(--b)),
var(--c) calc(100% - var(--b)) 99%,
#0000
) 50% / calc(100% / var(--f)) 100% no-repeat;
transform: scale(var(--f));
transition: .5s;
}
img:hover {
--f: 1.35; /* hover scale */
}Since we need a circular bottom border, we added a border-radius on the bottom side, allowing the outline to match the curvature of the gradient.
The calculation used on outline-offset is a lot more straightforward than it looks. By default, outline is drawn outside of the element’s box. And in our case, we need it to overlap the element. More precisely, we need it to follow the circle created by the gradient.
When we scale the element, we see the space between the circle and the edge. Let’s not forget that the idea is to keep the circle at the same size after the scale transformation runs, which leaves us with the space we will use to define the outline’s offset as illustrated in the above figure.
Let’s not forget that the second element is scaled, so our result is also scaled… which means we need to divide the result by f to get the real offset value:
Offset = ((f - 1) * S/2) / f = (1 - 1/f) * S/2We add a negative sign since we need the outline to go from the outside to the inside:
Offset = (1/f - 1) * S/2Here’s a quick demo that shows how the outline follows the gradient:
You may already see it, but we still need the bottom outline to overlap the circle rather than letting it bleed through it. We can do that by removing the border’s size from the offset:
outline-offset: calc((1 / var(--f) - 1) * var(--s) / 2) - var(--b));Now we need to find how to remove the top part from the outline. In other words, we only want the bottom part of the image’s outline.
First, let’s add space at the top with padding to help avoid the overlap at the top:
img {
--s: 280px; /* image size */
--b: 5px; /* border thickness */
--c: #C02942; /* border color */
--f: 1; /* initial scale */
width: var(--s);
aspect-ratio: 1;
padding-block-start: calc(var(--s)/5);
/* etc. */
}
img:hover {
--f: 1.35; /* hover scale */
}There is no particular logic to that top padding. The idea is to ensure the outline doesn’t touch the avatar’s head. I used the element’s size to define that space to always have the same proportion.
Note that I have added the content-box value to the background:
background:
radial-gradient(
circle closest-side,
#ECD078 calc(99% - var(--b)),
var(--c) calc(100% - var(--b)) 99%,
#0000
) 50%/calc(100%/var(--f)) 100% no-repeat content-box;We need this because we added padding and we only want the background set to the content box, so we must explicitly tell the background to stop there.
We reached the last part! All we need to do is to hide some pieces, and we are done. For this, we will rely on the mask property and, of course, gradients.
Here is a figure to illustrate what we need to hide or what we need to show to be more accurate
The left image is what we currently have, and the right is what we want. The green part illustrates the mask we must apply to the original image to get the final result.
We can identify two parts of our mask:
Here’s our final CSS:
img {
--s: 280px; /* image size */
--b: 5px; /* border thickness */
--c: #C02942; /* border color */
--f: 1; /* initial scale */
--_g: 50% / calc(100% / var(--f)) 100% no-repeat content-box;
--_o: calc((1 / var(--f) - 1) * var(--s) / 2 - var(--b));
width: var(--s);
aspect-ratio: 1;
padding-top: calc(var(--s)/5);
cursor: pointer;
border-radius: 0 0 999px 999px;
outline: var(--b) solid var(--c);
outline-offset: var(--_o);
background:
radial-gradient(
circle closest-side,
#ECD078 calc(99% - var(--b)),
var(--c) calc(100% - var(--b)) 99%,
#0000) var(--_g);
mask:
linear-gradient(#000 0 0) no-repeat
50% calc(-1 * var(--_o)) / calc(100% / var(--f) - 2 * var(--b)) 50%,
radial-gradient(
circle closest-side,
#000 99%,
#0000) var(--_g);
transform: scale(var(--f));
transition: .5s;
}
img:hover {
--f: 1.35; /* hover scale */
}Let’s break down that mask property. For starters, notice that a similar radial-gradient() from the background property is in there. I created a new variable, --_g, for the common parts to make things less cluttered.
--_g: 50% / calc(100% / var(--f)) 100% no-repeat content-box;
mask:
radial-gradient(
circle closest-side,
#000 99%,
#0000) var(--_g);Next, there’s a linear-gradient() in there as well:
--_g: 50% / calc(100% / var(--f)) 100% no-repeat content-box;
mask:
linear-gradient(#000 0 0) no-repeat
50% calc(-1 * var(--_o)) / calc(100% / var(--f) - 2 * var(--b)) 50%,
radial-gradient(
circle closest-side,
#000 99%,
#0000) var(--_g);This creates the rectangle part of the mask. Its width is equal to the radial gradient’s width minus twice the border thickness:
calc(100% / var(--f) - 2 * var(--b))The rectangle’s height is equal to half, 50%, of the element’s size.
We also need the linear gradient placed at the horizontal center (50%) and offset from the top by the same value as the outline’s offset. I created another CSS variable, --_o, for the offset we previously defined:
--_o: calc((1 / var(--f) - 1) * var(--s) / 2 - var(--b));One of the confusing things here is that we need a negative offset for the outline (to move it from outside to inside) but a positive offset for the gradient (to move from top to bottom). So, if you’re wondering why we multiply the offset, --_o, by -1, well, now you know!
Here is a demo to illustrate the mask’s gradient configuration:
Hover the above and see how everything move together. The middle box illustrates the mask layer composed of two gradients. Imagine it as the visible part of the left image, and you get the final result on the right!
Oof, we’re done! And not only did we wind up with a slick hover animation, but we did it all with a single HTML <img> element. Just that and less than 20 lines of CSS trickery!
Sure, we relied on some little tricks and math formulas to reach such a complex effect. But we knew exactly what to do since we identified the pieces we needed up-front.
Could we have simplified the CSS if we allowed ourselves more HTML? Absolutely. But we’re here to learn new CSS tricks! This was a good exercise to explore CSS gradients, masking, the outline property’s behavior, transformations, and a whole bunch more. If you felt lost at any point, then definitely check out my series that uses the same general concepts. It sometimes helps to see more examples and use cases to drive a point home.
I will leave you with one last demo that uses photos of popular CSS developers. Don’t forget to show me a demo with your own image so I can add it to the collection!
A Fancy Hover Effect For Your Avatar originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.
