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6/30/2026
A Practical CSS Variable Setup for Light/Dark Mode Without Theme Flash

A Practical CSS Variable Setup for Light/Dark Mode Without Theme Flash

Short summary

This tutorial demonstrates a practical approach to implementing light/dark mode using CSS variables and localStorage without theme-flash problems on page load. An inline script in <head> runs before CSS parsing to apply stored user preferences, preventing visual flashing. Complete code examples show semantic color variables, system preference detection via prefers-color-scheme, and a simple toggle implementation.

  • •CSS variables + localStorage + inline <head> script prevent theme flash
  • •Respects system dark-mode preference unless user explicitly selects light
  • •Ready-to-use code examples for semantic variables and theme toggle button

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