Theme variables without a preprocessor
Sass and LESS variables compile to static values. Custom properties live in the browser and can change at runtime.
2 --primary: #7c3aed;
3 --spacing: 16px;
4}
5.btn { background: var(--primary); }
2$primary: #7c3aed;
3$spacing: 16px;
4
5.btn {
6 background: $primary;
7}
// Output is static. Change theme = recompile.
Browser Support for CSS custom properties
This feature is well established and works across many devices and browser versions. It has been available across browsers since 2017.
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Runtime updates
Change --primary in JS or a class and every use updates. No rebuild.
No build step
Plain CSS. Works in any environment, no Sass or LESS required.
Cascade and override
Set on :root, override in .dark or a component. Inherits like normal CSS.
How it works
Preprocessor variables like $primary: #7c3aed are replaced at compile time. The output is plain hex. To switch themes you recompile or generate multiple stylesheets.
Custom properties (--primary: #7c3aed) are real CSS. You read and set them with var(--primary). Toggle a class on the root or use JS to change --primary and every reference updates. No build, no duplicate CSS.