Reactivity
Globally Responsive
CSS variables can be changed inside media queries. And by redefining a variable on
:root in a media query, that variable will be globally responsive.1
@media (max-width: 45em) {
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:root {
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--size-5: var(--size-4);
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}
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}
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Javascript Interactivity
CSS variables can also be accessed and updated in JavaScript, which allows you to accomplish things that were previously very complicated, like dynamically applying style themes. By updating a few key variables based on user input, you can reskin an entire interface.
Update CSS variables in JS by using the
setProperty method on the document root’s style property.1
document.documentElement.style.setProperty(`--color-primary`, `#4299e1`);
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You can also alias variables to other variables, this is useful for using a consistent property throughout your codebase that can be dynamically updated without losing meaning.
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function enableDarkMode() {
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document.documentElement.style.setProperty(`--color-background`, `var(--color-black)`);
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document.documentElement.style.setProperty(`--color-text`, `white`)
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}
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