Dynamic Theming with CSS: Light, Dark, and Custom
How to implement dynamic CSS theming using custom properties and JavaScript. Covers light/dark mode, user preferences, and runtime switching.
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Tags: css, color, developer-tools
Dynamic Theming with CSS: Build Light, Dark, and Custom Themes A well-built theme system should do three things: respond to the user's OS preference by default, allow the user to override that preference, and make it trivially easy to add new themes in the future. Getting all three right requires a specific architecture. This post builds a complete theme system from scratch — CSS token structure, attribute switching, JavaScript toggle logic, system preference detection, and a custom theme override pattern. The implementation is framework-agnostic but the React integration example is included. --- Architecture Overview The cleanest theme system uses three layers: CSS custom properties for all color values — no hardcoded colors in component CSS A attribute on — determines which token values…
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