What Can We Actually Do With corner-shape?

When I first started messing around with code, rounded corners required five background images or an image sprite likely created in Photoshop, so when border-radius came onto the scene, I remember everybody thinking that it was the best thing ever. Web designs were very square at the time, so to have border-radius was super cool, and it saved us a lot of time, too.

Chris’ border-radius article from 2009, which at the time of writing is 16 years old (wait, how old am I?!), includes vendor prefixes for older web browsers, including “old Konqueror browsers” (-khtml-border-radius). What a time to be alive!

We’re much less excited about rounded corners nowadays. In fact, sharp corners have made a comeback and are just as popular now, as are squircles (square-ish circles or circle-y squares, take your pick), which is exactly what the corner-shape CSS property enables us to create (in addition to many other cool UI effects that I’ll be walking you through today).

At the time of writing, only Chrome 139 and above supports corner-shape, which must be used with the border-radius property or/and any of the related individual properties (i.e., border-top-left-radius, border-top-right-radius, border-bottom-right-radius, and border-bottom-left-radius):

Snipped corners using corner-shape: bevel

These snipped corners are becoming more and more popular as UI designers embrace brutalist aesthetics.

In the example above, it’s as easy as using corner-shape: bevel for the snipped corners effect and then border-bottom-right-radius: 16px for the size.

corner-shape: bevel;
border-bottom-right-radius: 16px;

We can do the same thing and it really works with a cyberpunk aesthetic:

Slanted sections using corner-shape: bevel

Slanted sections is a visual effect that’s even more popular, probably not going anywhere, and again, helps elements to look a lot less like the boxes that they are.

Before we dive in though, it’s important to keep in mind that each border radii has two semi-major axes, a horizontal axis and a vertical axis, with a ‘point’ (to use vector terminology) on each axis. In the example above, both are set to 16px, so both points move along their respective axis by that amount, away from their corner of course, and then the beveled line is drawn between them. In the slanted section example below, however, we need to supply a different point value for each axis, like this:

corner-shape: bevel;
border-bottom-right-radius: 100% 50px;

The first point moves along 100% of the horizontal axis whereas the second point travels 50px of the vertical axis, and then the beveled line is drawn between them, creating the slant that you see above.

By the way, having different values for each axis and border radius is exactly how those cool border radius blobs are made.

Sale tags using corner-shape: round bevel bevel round

You’ve see those sale tags on almost every e-commerce website, either as images or with rounded corners and not the pointy part (other techniques just aren’t worth the trouble). But now we can carve out the proper shape using two different types of corner-shape at once, as well as a whole set of border radius values:

You’ll need corner-shape: round bevel bevel round to start off. The order flows clockwise, starting from the top-left, as follows:

• top-left
• top-right
• bottom-right
• bottom-left

Just like with border-radius. You can omit some values, causing them to be inferred from other values, but both the inference logic and resulting value syntax lack clarity, so I’d just avoid this, especially since we’re about to explore a more complex border-radius:

corner-shape: round bevel bevel round;
border-radius: 16px 48px 48px 16px / 16px 50% 50% 16px;

Left of the forward slash (/) we have the horizontal-axis values of each corner in the order mentioned above, and on the right of the /, the vertical-axis values. So, to be clear, the first and fifth values correspond to the same corner, as do the second and sixth, and so on. You can unpack the shorthand if it’s easier to read:

border-top-left-radius: 16px;
border-top-right-radius: 48px 50%;
border-bottom-right-radius: 48px 50%;
border-bottom-left-radius: 16px;

Up until now, we’ve not really needed to fully understand the border radius syntax. But now that we have corner-shape, it’s definitely worth doing so.

As for the actual values, 16px corresponds to the round corners (this one’s easy to understand) while the 48px 50% values are for the bevel ones, meaning that the corners are ‘drawn’ from 48px horizontally to 50% vertically, which is why and how they head into a point.

Regarding borders — yes, the pointy parts would look nicer if they were slightly rounded, but using borders and outlines on these elements yields unpredictable (but I suspect intended) results due to how browsers draw the corners, which sucks.

Arrow crumbs using the same method

Yep, same thing.

We essentially have a grid row with negative margins, but because we can’t create ‘inset’ arrows or use borders/outlines, we have to create an effect where the fake borders of certain arrows bleed into the next. This is done by nesting the exact same shape in the arrows and then applying something to the effect of padding-right: 3px, where 3px is the value of the would-be border. The code comments below should explain it in more detail (the complete code in the Pen is quite interesting, though):

<nav>
  <ol>
    <li>
      <a>Step 1</a>
    </li>
    <li>
      <a>Step 2</a>
    </li>
    <li>
      <a>Step 3</a>
    </li>
  </ol>
</nav>

ol {
  /* Clip n’ round */
  overflow: clip;
  border-radius: 16px;

  li {
    /* Arrow color */
    background: hsl(270 100% 30%);

    /* Reverses the z-indexes, making the arrows stack */
    /* Result: 2, 1, 0, ... (sibling-x requires Chrome 138+) */
    z-index: calc((sibling-index() * -1) + sibling-count());

    &:not(:last-child) {
      /* Arrow width */
      padding-right: 3px;

      /* Arrow shape */
      corner-shape: bevel;
      border-radius: 0 32px 32px 0 / 0 50% 50% 0;

      /* Pull the next one into this one */
      margin-right: -32px;

    }

    a {
      /* Same shape */
      corner-shape: inherit;
      border-radius: inherit;

      /* Overlay background */
      background: hsl(270 100% 50%);
    }
  }
}

Tooltips using corner-shape: scoop

To create this tooltip style, I’ve used a popover, anchor positioning (to position the caret relative to the tooltip), and corner-shape: scoop. The caret shape is the same as the arrow shape used in the examples above, so feel free to switch scoop to bevel if you prefer the classic triangle tooltips.

A quick walkthrough:

<!-- Connect button to tooltip -->
<button popovertarget="tooltip" id="button">Click for tip</button>

<!-- Anchor tooltip to button -->
<div anchor="button" id="tooltip" popover>Don’t eat yellow snow</div>

#tooltip {
  /* Define anchor */
  anchor-name: --tooltip;

  /* Necessary reset */
  margin: 0;

  /* Center vertically */
  align-self: anchor-center;

  /* Pin to right side + 15 */
  left: calc(anchor(right) + 15px);

  &::after {
    /* Create caret */
    content: "";
    width: 5px;
    height: 10px;
    corner-shape: scoop;
    border-top-left-radius: 100% 50%;
    border-bottom-left-radius: 100% 50%;

    /* Anchor to tooltip */
    position-anchor: --tooltip;

    /* Center vertically */
    align-self: anchor-center;

    /* Pin to left side */
    right: anchor(left);

    /* Popovers have this already (required otherwise) */
    position: fixed;
  }
}

If you’d rather these were hover-triggered, the upcoming Interest Invoker API is what you’re looking for.

Realistic highlighting using corner-shape: squircle bevel

The <mark> element, used for semantic highlighting, defaults with a yellow background, but it doesn’t exactly create a highlighter effect. By adding the following two lines of CSS, which admittedly I discovered by experimenting with completely random values, we can make it look more like a hand-waved highlight:

mark {
  /* A...squevel? */
  corner-shape: squircle bevel;
  border-radius: 50% / 1.1rem 0.5rem 0.9rem 0.7rem;

  /* Prevents background-break when wrapping */
  box-decoration-break: clone;
}

We can also use squircle by itself to create those fancy-rounded app icons, or use them on buttons/cards/form controls/etc. if you think the ‘old’ border radius is starting to look a bit stale:

Hand-drawn boxes using the same method

Same thing, only larger. Kind of looks like a hand-drawn box?

Admittedly, this effect doesn’t look as awesome on a larger scale, so if you’re really looking to wow and create something more akin to the Red Dead Redemption aesthetic, this border-image approach would be better.

Clip a background with corner-shape: notch

Notched border radii are ugly and I won’t hear otherwise. I don’t think you’ll want to use them to create a visual effect, but I’ve learned that they’re useful for background clipping if you set the irrelevant axis to 50% and the axis of the side that you want to clip by the amount that you want to clip it by. So if you wanted to clip 30px off the background from the left for example, you’d choose 30px for the horizontal axes and 50% for the vertical axes (for the -left-radius properties only, of course).

corner-shape: notch;
border-top-left-radius: 30px 50%;
border-bottom-left-radius: 30px 50%;

Conclusion

So, corner-shape is actually a helluva lot of fun. It certainly has more uses than I expected, and no doubt with some experimentation you’ll come up with some more. With that in mind, I’ll leave it to you CSS-Tricksters to mess around with (remember though, you’ll need to be using Chrome 139 or higher).

As a parting gift, I leave you with this very cool but completely useless CSS Tie Fighter, made with corner-shape and anchor positioning:

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September 12, 2025 at 10:02AM

Compiling Multiple CSS Files into One

Stu Robson is on a mission to “un-Sass” his CSS. I see articles like this pop up every year, and for good reason as CSS has grown so many new legs in recent years. So much so that much of the core features that may have prompted you to reach for Sass in the past are now baked directly into CSS. In fact, we have Jeff Bridgforth on tap with a related article next week.

What I like about Stu’s stab at this is that it’s an ongoing journey rather than a wholesale switch. In fact, he’s out with a new post that pokes specifically at compiling multiple CSS files into a single file. Splitting and organizing styles into separate files is definitely the reason I continue to Sass-ify my work. I love being able to find exactly what I need in a specific file and updating it without having to dig through a monolith of style rules.

But is that a real reason to keep using Sass? I’ve honestly never questioned it, perhaps due to a lizard brain that doesn’t care as long as something continues to work. Oh, I want partialized style files? Always done that with a Sass-y toolchain that hasn’t let me down yet. I know, not the most proactive path.

Stu outlines two ways to compile multiple CSS files when you aren’t relying on Sass for it:

Using PostCSS

Ah, that’s right, we can use PostCSS both with and without Sass. It’s easy to forget that PostCSS and Sass are compatible, but not dependent on one another.

postcss main.css -o output.css

Stu explains why this could be a nice way to toe-dip into un-Sass’ing your work:

PostCSS can seamlessly integrate with popular build tools like webpack, Gulp, and Rollup, allowing you to incorporate CSS compilation into your existing development workflow without potential, additional configuration headaches.

Custom Script for Compilation

The ultimate thing would be eliminating the need for any dependencies. Stu has a custom Node.js script for that:

const fs = require('fs');
const path = require('path');
// Function to read and compile CSS
function compileCSS(inputFile, outputFile) {
    const cssContent = fs.readFileSync(inputFile, 'utf-8');
    const imports = cssContent.match(/@import\s+['"]([^'"]+)['"]/g) || [];
    let compiledCSS = '';
    // Read and append each imported CSS file
    imports.forEach(importStatement => {
        const filePath = importStatement.match(/['"]([^'"]+)['"]/)[1];
        const fullPath = path.resolve(path.dirname(inputFile), filePath);
        compiledCSS += fs.readFileSync(fullPath, 'utf-8') + '\n';
    });
    // Write the compiled CSS to the output file
    fs.writeFileSync(outputFile, compiledCSS.trim());
    console.log(`Compiled CSS written to ${outputFile}`);
}
// Usage
const inputCSSFile = 'index.css'; // Your main CSS file
const outputCSSFile = 'output.css'; // Output file
compileCSS(inputCSSFile, outputCSSFile);

Not 100% free of dependencies, but geez, what a nice way to reduce the overhead and still combine files:

node compile-css.js

This approach is designed for a flat file directory. If you’re like me and prefer nested subfolders:

With the flat file structure and single-level import strategy I employ, nested imports (you can do with postcss-import aren’t necessary for my project setup, simplifying the compilation process while maintaining clean organisation.

Very cool, thanks Stu! And check out the full post because there’s a lot of helpful context behind this, particularly with the custom script.

---

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What’re Your Top 4 CSS Properties?

That’s what Donnie D’Amato asks in a recent post:

You are asked to build a website but you can use only 4 CSS properties, what are those?

This really got the CSS-Tricks team talking. It’s the nerdy version of “if you could only take one album with you on a remote island…” And everyone had a different opinion which is great because it demonstrates the messy, non-linear craft that is thinking like a front-end developer.

Seems like a pretty straightforward thing to answer, right? But like Donnie says, this takes some strategy. Like, say spacing is high on your priority list. Are you going to use margin? padding? Perhaps you’re leaning into layout and go with gap as part of a flexbox direction… but then you’re committing to display as one of your options. That can quickly eat up your choices!

Our answers are pretty consistent, but converged even more as the discussion wore on and all of us were coming at it with different priorities. I’ll share each person’s “gut” reaction because I like how raw it is. I think you’ll see that there’s always a compromise in the mix, but those compromises really reveal a person’s cards as far as what they think is most important in a situation with overly tight constraints.

---

Juan Diego Rodriguez

Juan and I came out pretty close to the same choices, as we’ll see in a bit:

• font: Typography is a priority and we get a lot of constituent properties with this single shorthand.
• padding: A little padding makes things breath and helps with visual separation.
• background: Another shorthand with lots of styling possibilities in a tiny package.
• color: More visual hierarchy.

But he was debating with himself a bit in the process:

Thinking about switching color with place-items, since it works in block elements. grid would need display, though).

Ryan Trimble

Ryan’s all about that bass structure:

• display: This opens up a world of layouts, but most importantly flex.
• flex-direction: It’s a good idea to consider multi-directional layouts that are easily adjustable with media queries.
• width: This helps constrain elements and text, as well as divide up flex containers.
• margin: This is for spacing that’s bit more versatile than gap, while also allowing us to center elements easily.

And Ryan couldn’t resist reaching a little out of bounds:

For automatic color theme support, and no extra CSS properties required: <meta name="color-scheme" content="dark light"> 

Danny Schwarz

Every team needs a wild card:

On the contrary I think I’d choose font, padding, and color. I wouldn’t even choose a 4th.

• font: This isn’t a big surprise if you’re familiar with Danny’s writing.
• padding: So far, Ryan’s the only one to eschew padding as a core choice!
• color: Too bad this isn’t baked right into font!

I’ll also point out that Danny soon questioned his decision to use all four choices:

I supposed we’d need width to achieve a good line length.

Sunkanmi Fafowora

This is the first list to lean squarely into CSS Grid, allowing the grid shorthand to take up a choice in favor of having a complete layout system:

• font: This is a popular one, right?
• display: Makes grid available
• grid: Required for this display approach
• color: For sprinkling in text color where it might help

I love that Ryan and Sunkanmi are thinking in terms of structure, albeit in very different ways for different reasons!

Zell Liew

In Zell’s own words: “Really really plain and simple site here.”

• font: Content is still the most important piece of information.
• max-width: Ensures type measure is ok.
• margin: Lets me play around with spacing.
• color: This ensures there’s no pure black/white contrast that hurts the eyes. I’d love for background as well, but we only have four choices.

But there’s a little bit of nuance in those choices, as he explains: “But I’d switch up color for background on sites with more complex info that requires proper sectioning. In that case I’d also switch margin with padding.”

Amit Sheen

Getting straight to Amit’s selections:

• font
• color
• background
• color-scheme

The choices are largely driven by wanting to combat default user agent styles:

The thing is, if we only have four properties, we end up relying heavily on the user agents, and the only thing I’d really want to change is the fonts. But while we are at it, let’s add some color control. I’m not sure how much I’d actually use them, but it would be good to have them available.

Geoff Graham

Alright, I’m not quite as exciting now that you’ve seen everyone else’s choices. You’ll see a lot of overlap here:

• font: A shorthand for a whopping SEVEN properties for massaging text styles.
• color: Seems like this would come in super handy for establishing a visual hierarchy and distinguishing one element from another.
• padding: I can’t live without a little breathing room between an element’s content box and its inner edge.
• color-scheme: Good minimal theming that’ll work nicely alongside color and support the light-dark() function.

Clearly, I’m all in on typography. That could be a very good thing or it could really constrain me when it comes to laying things out. I really had to fight the urge to use display because I always find it incredibly useful for laying things out side-by-side that wouldn’t otherwise be possible with block-level elements.

---

Your turn!

Curious minds want to know! Which four properties would you take with you on a desert island?

---

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