custom properties

Let's say you wanted to move the background-position on an element as you mouse over it to give the design a little pizzazz. You have an element like this:

<div class="module" id="module"></div>

And you toss a background on it:

.module {
  background-image: url(big-image.jpg);
}

You can adjust the background-position in JavaScript like this:

const el = document.querySelector("#module");

el.addEventListener("mousemove", (e) => {
  el.style.backgroundPositionX = -e.offsetX + "px";
  el.style.backgroundPositionY = -e.offsetY + "px";
});

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Here's a CSS variable (formally called a "CSS custom property"):

:root {
  --mouse-x: 0px;
  --mouse-y: 0px;
}

Perhaps you use them to set a position:

.mover {
  left: var(--mouse-x);
  top: var(--mouse-y);
}

To update those values from JavaScript, you'd:

let root = document.documentElement;

root.addEventListener("mousemove", e => {
  root.style.setProperty('--mouse-x', e.clientX + "px");
  root.style.setProperty('--mouse-y', e.clientY + "px");
});

That's all.

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A little while ago, I wrote a well-received article about combining CSS variables with CSS grid to help build more maintainable layouts. But CSS grid isn’t just for pages! That is a common myth. Although it is certainly very useful for page layout, I find myself just as frequently reaching for grid when it comes to components. In this article I’ll address using CSS grid at the component level.

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I got the idea for doing something of the kind when I stumbled across this interactive SVG pie chart. While the SVG code is as compact as it gets (a single <circle></circle> element!), using strokes for creating pie chart slices is problematic as we run into rendering issues on Windows for Firefox and Edge. Plus, in 2018, we can accomplish a lot more with a lot less JavaScript!

I managed to get the following result using a single HTML element for the chart and very little JavaScript. The future should completely eliminate the need for any JavaScript, but more on that later.

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I first got the idea to CSS something of the kind when I saw this gradient infinity logo by Infographic Paradise. The gradient doesn't look like in the original illustration, as I chose to generate the rainbow logically instead of using the Dev Tools picker or something like that, but other than that, I think I got pretty close—let's see how I did that!

We were all introduced to the env() function in CSS when all that drama about "The Notch" and the iPhone X was going down. The way that Apple landed on helping us move content away from those "unsafe" areas was to provide us essentially hard-coded variables to use:

padding: 
  env(safe-area-inset-top) 
  env(safe-area-inset-right) 
  env(safe-area-inset-bottom) 
  env(safe-area-inset-left);

Uh ok! Weird! Now, nine months later, an "Unofficial Proposal Draft" for env() has landed. This is how specs work, as I understand it. Sometimes browser vendors push forward with stuff they need, and then it's standardized. It's not always waiting around for standards bodies to invent things and then browser vendors implementing those things.

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I've been playing with CSS transforms for over five years and one thing that has always bugged me was that I couldn't animate the components of a transform chain individually. This article is going to explain the problem, the old workaround, the new magic Houdini solution and, finally, will offer you a feast of eye candy through better looking examples than those used to illustrate concepts.

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I recently came across this Pen and my first thought was that it could all be done with just three elements: a wrapper, a range input and an output. On the CSS side, this involves using a conic-gradient() with a stop set to a CSS variable.

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