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CSS Variables (Custom Properties)

 

CSS Variables, also known as Custom Properties, let you store values — like colors, fonts, or sizes — in reusable variables. This makes your CSS more maintainable, consistent, and easier to update across large projects.

Why Use CSS Variables?

  • Define a value once and reuse it multiple times.
  • Easily update the design by changing the variable value.
  • Create themes by switching variable values dynamically.
  • Improve code readability.

How to Define and Use CSS Variables

CSS variables are declared inside a selector (commonly :root for global scope) using the syntax --variable-name: value;

Example:

:root {

  --main-color: #3498db;

  --font-size: 16px;

}

 

body {

  color: var(--main-color);

  font-size: var(--font-size);

}

Key Points

  • Use the var() function to access the variable value.
  • Variables can inherit and cascade like normal CSS properties.
  • You can provide fallback values: var(--variable, fallback).
  • Variables can be updated dynamically with JavaScript.

Example: Theming with CSS Variables

:root {

  --background: white;

  --text-color: black;

}

 

.dark-theme {

  --background: #222;

  --text-color: #eee;

}

 

body {

  background-color: var(--background);

  color: var(--text-color);

}

Toggling the .dark-theme class on the body switches the color scheme easily.

CSS Variables empower you to write cleaner, more flexible CSS and build adaptable designs without repetitive code.

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