A Brief Intro to CSS Variables (Custom Properties)

Variables in pure CSS without a preprocessor of any kind are available today in most modern browsers. They are officially called custom properties and allow avoiding much of the repetition involved with traditional CSS, and, contrary to variables with preprocessors, they can be changed dynamically.

Here’s how to use custom properties:

/* Declaration */
some-element {
  --my-bg-color: #F9EC31;
}

/* Using it */
some-element {
  background-color: var(--my-bg-color);
}

You can also provide a fallback value when using a variable, which will be used if the variable hasn’t been defined:

some-element {
  background-color: var(--my-bg-color, papayawhip);
}

:root

A common use case is to define variables in the :root pseudo-class and then use it anywhere the value is needed:

:root {
  --funky-shadow: 3px 3px 10px brown;
}

.ugly-box {
  box-shadow: var(--funky-shadow);
}

Calc()

You can also use calc() on variable values:

:root {
  --special-padding: 1.5em;
}

.pandora-box {
  padding-bottom: calc(var(--special-padding) + 1em);
}

Browser Support

👉 Myth is a good option to start using CSS variables today.

Can I Use css-variables? Data on support for the css-variables feature across the major browsers from caniuse.com.

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