How to Define Colors as Variables in Css

Creating CSS Global Variables : Stylesheet theme management

Latest Update: 16/01/2020

CSS Custom Properties (Variables) have arrived!

It's 2020 and time to officially roll out this feature in your new applications.

Preprocessor "NOT" required!

There is a lot of repetition in CSS. A single color may be used in several places.

For some CSS declarations, it is possible to declare this higher in the cascade and let CSS inheritance solve this problem naturally.

For non-trivial projects, this is not always possible. By declaring a variable on the :root pseudo-element, a CSS author can halt some instances of repetition by using the variable.

How it works

Set your variable at the top of your stylesheet:


Create a root class:

:root {

Create variables (-- [String] : [value])

:root {
--red: #b00;
--blue: #00b;
--fullwidth: 100%;

Set your variables anywhere in your CSS document:

h1 {
color: var(--red);
#MyText {
color: var(--blue);
width: var(--fullwidth);


See for current compatability.

![supported browsers

Firefox: Version 31+ (Enabled by default)

Supported since 2014 (Leading the way as usual.)

More info from Mozilla

Chrome: Version 49+ (Enabled by default).

Supported since 2016

Safari/IOS Safari: Version 9.1/9.3 (Enabled by default).

Supported since 2016

Opera: Version 39+ (Enabled by default).

Supported since 2016

Android: Version 52+ (Enabled by default).

Supported since 2016

Edge: Version 15+ (Enabled by default).

Supported since 2017

CSS Custom Properties landed in Windows Insider Preview build 14986

IE: When pigs fly.

It's time to finally let this ship sink. No one enjoyed riding her anyway. ☺


Full specification for upcoming CSS variables

Read more


A fiddle and snippet are attached below for testing:

(It will only work with supported browsers.)


:root {
--red: #b00;
--blue: #4679bd;
--grey: #ddd;
--W200: 200px;
--Lft: left;
.Bx4 {
float: var(--Lft);
width: var(--W200);
height: var(--W200);
margin: 10px;
padding: 10px;
border: 1px solid var(--red);
.Bx1 {
color: var(--red);
background: var(--grey);
.Bx2 {
color: var(--grey);
background: black;
.Bx3 {
color: var(--grey);
background: var(--blue);
.Bx4 {
color: var(--grey);
background: var(--red);
<p>If you see four square boxes then variables are working as expected.</p>

<div class="Bx1">I should be red text on grey background.</div>
<div class="Bx2">I should be grey text on black background.</div>
<div class="Bx3">I should be grey text on blue background.</div>
<div class="Bx4">I should be grey text on red background.</div>

How to use css variable colors and js to change div background

You can add a data-color attribute to your buttons which specifies the color (variable) to change to when clicking on the given button. Then you can add the click event listener to all your buttons with the class color-btn. Then when you click on a given button the event listener will be called, which will get the data attribute from the button clicked, and then use your changeColor function to change the div to the appropriate color (using the variable).

Also, you haven't defined your variables correctly. Firstly, you need to target the root using :root. Then you nee to set your variables using --variableName: COLOR. Lastly, in your changeColor function you need to use .style.backgroundColor = "var(--" +color +")" to correctly use the variable.

See working example below

[...document.getElementsByClassName("color-btn")].forEach(elem => {  elem.addEventListener('click', function() {    const btnColor = this.getAttribute('data-color');    changeColor(btnColor);  });})
function changeColor(color) { var element = document.getElementById('box'); = "var(--" +color +")";}
:root {  --w: #fff;  --b: #000;}
.box { width: 100px; height: 100px; border: 1px solid #aaa; background-color: #fff;}
<script src=""></script><div class="box" id="box"></div>
<button class="color-btn" data-color='w'>white</button><button class="color-btn" data-color='b'>black</button>

How to create color shades using CSS variables similar to darken() of Sass?

The new Specification introduces "relative color syntax" where you can do the following

:root {
--color-primary: #f00; /* any format you want here */
--color-primary-darker: hsl(from var(--color-primary) h s calc(l - 5%));
--color-primary-darkest: hsl(from var(--color-primary) h s calc(l - 10%));

The idea is to convert the main color to hsl format and using calc() you adjust the lightness.

There is still no support for this to date so consider the below solution.

You can consider hsl() colors and simply control the lightness: