CSS Variables – The var() Function

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CSS Variables

The var() function is used to insert the value of a CSS variable.

CSS variables have access to the DOM, which means that you can create variables with local or global scope, change the variables with JavaScript, and change the variables based on media queries.

A good way to use CSS variables is when it comes to the colors of your design. Instead of copy and paste the same colors over and over again, you can place them in variables.

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The Traditional Way

The following example shows the traditional way of defining some colors in a style sheet (by defining the colors to use, for each specific element):

Example

body { background-color: #1e90ff; }

h2 { border-bottom: 2px solid #1e90ff; }

.container {
  color: #1e90ff;
  background-color: #ffffff;
  padding: 15px;
}

button {
  background-color: #ffffff;
  color: #1e90ff;
  border: 1px solid #1e90ff;
  padding: 5px;
}

Try it Yourself »

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Syntax of the var() Function

The var() function is used to insert the value of a CSS variable.

The syntax of the var() function is as follows:

var(–name, value)

Value	Description
name	Required. The variable name (must start with two dashes)
value	Optional. The fallback value (used if the variable is not found)

Note: The variable name must begin with two dashes (–) and it is case sensitive!

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How var() Works

First of all: CSS variables can have a global or local scope.

Global variables can be accessed/used through the entire document, while local variables can be used only inside the selector where it is declared.

To create a variable with global scope, declare it inside the :root selector. The :root selector matches the document’s root element.

To create a variable with local scope, declare it inside the selector that is going to use it.

The following example is equal to the example above, but here we use the var() function.

First, we declare two global variables (–blue and –white). Then, we use the var() function to insert the value of the variables later in the style sheet:

Example

:root {
  –blue: #1e90ff;
  –white: #ffffff;
}

body { background-color: var(–blue); }

h2 { border-bottom: 2px solid var(–blue); }

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
}

button {
  background-color: var(–white);
  color: var(–blue);
  border: 1px solid var(–blue);
  padding: 5px;
}

Try it Yourself »

Advantages of using var() are:

• makes the code easier to read (more understandable)
• makes it much easier to change the color values

To change the blue and white color to a softer blue and white, you just need to change the two variable values:

Example

:root {
  –blue: #6495ed;
  –white: #faf0e6;
}

body { background-color: var(–blue); }

h2 { border-bottom: 2px solid var(–blue); }

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
}

button {
  background-color: var(–white);
  color: var(–blue);
  border: 1px solid var(–blue);
  padding: 5px;
}

Try it Yourself »

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Browser Support

The numbers in the table specify the first browser version that fully supports the var() function.

Function
var()	49.0	15.0	31.0	9.1	36.0

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CSS var() Function

Property	Description
var()	Inserts the value of a CSS variable

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CSS Overriding Variables

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Override Global Variable With Local Variable

From the previous page we have learned that global variables can be accessed/used through the entire document, while local variables can be used only inside the selector where it is declared.

Look at the example from the previous page:

Example

:root {
  –blue: #1e90ff;
  –white: #ffffff;
}

body {
  background-color: var(–blue);
}

h2 {
  border-bottom: 2px solid var(–blue);
}

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
}

button {
  background-color: var(–white);
  color: var(–blue);
  border: 1px solid var(–blue);
  padding: 5px;
}

Try it Yourself »

Sometimes we want the variables to change only in a specific section of the page.

Assume we want a different color of blue for button elements. Then, we can re-declare the –blue variable inside the button selector. When we use var(–blue) inside this selector, it will use the local –blue variable value declared here.

We see that the local –blue variable will override the global –blue variable for the button elements:

Example

:root {
  –blue: #1e90ff;
  –white: #ffffff;
}

body {
  background-color: var(–blue);
}

h2 {
  border-bottom: 2px solid var(–blue);
}

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
}

button {
  –blue: #0000ff; /* local variable will override global */
  background-color: var(–white);
  color: var(–blue);
  border: 1px solid var(–blue);
  padding: 5px;
}

Try it Yourself »

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Add a New Local Variable

If a variable is to be used at only one single place, we could also have declared a new local variable, like this:

Example

:root {
  –blue: #1e90ff;
  –white: #ffffff;
}

body {
  background-color: var(–blue);
}

h2 {
  border-bottom: 2px solid var(–blue);
}

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
}

button {
  –button-blue: #0000ff; /* new local variable */
  background-color: var(–white);
  color: var(–button-blue);
  border: 1px solid var(–button-blue);
  padding: 5px;
}

Try it Yourself »

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Browser Support

The numbers in the table specify the first browser version that fully supports the var() function.

Function
var()	49.0	15.0	31.0	9.1	36.0

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CSS var() Function

Property	Description
var()	Inserts the value of a CSS variable

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CSS Change Variables With JavaScript

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Change Variables With JavaScript

CSS variables have access to the DOM, which means that you can change them with JavaScript.

Here is an example of how you can create a script to display and change the –blue variable from the example used in the previous pages. For now, do not worry if you are not familiar with JavaScript. You can learn more about JavaScript in our JavaScript Tutorial:

Example

<script>
// Get the root element
var r = document.querySelector(‘:root’);

// Create a function for getting a variable value
function myFunction_get() {
  // Get the styles (properties and values) for the root
  var rs = getComputedStyle(r);
  // Alert the value of the –blue variable
  alert(“The value of –blue is: ” + rs.getPropertyValue(‘–blue’));
}

// Create a function for setting a variable value
function myFunction_set() {
  // Set the value of variable –blue to another value (in this case “lightblue”)
  r.style.setProperty(‘–blue’, ‘lightblue’);
}
</script>

Try it Yourself »

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Browser Support

The numbers in the table specify the first browser version that fully supports the var() function.

Function
var()	49.0	15.0	31.0	9.1	36.0

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CSS var() Function

Property	Description
var()	Inserts the value of a CSS variable

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CSS Using Variables in Media Queries

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Using Variables in Media Queries

Now we want to change a variable value inside a media query.

Tip: Media Queries are about defining different style rules for different devices (screens, tablets, mobile phones, etc.). You can learn more Media Queries in our Media Queries Chapter.

Here, we first declare a new local variable named –fontsize for the .container class. We set its value to 25 pixels. Then we use it in the .container class further down. Then, we create a @media rule that says “When the browser’s width is 450px or wider, change the –fontsize variable value of the .container class to 50px.”

Here is the complete example:

Example

/* Variable declarations */
:root {
  –blue: #1e90ff;
  –white: #ffffff;
}

.container {
  –fontsize: 25px;
}

/* Styles */
body {
  background-color: var(–blue);
}

h2 {
  border-bottom: 2px solid var(–blue);
}

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
  font-size: var(–fontsize);
}

@media screen and (min-width: 450px) {
  .container {
    –fontsize: 50px;
  }
}

Try it Yourself »

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Here is another example where we also change the value of the –blue variable in the @media rule:

Example

/* Variable declarations */
:root {
  –blue: #1e90ff;
  –white: #ffffff;
}

.container {
  –fontsize: 25px;
}

/* Styles */
body {
  background-color: var(–blue);
}

h2 {
  border-bottom: 2px solid var(–blue);
}

.container {
  color: var(–blue);
  background-color: var(–white);
  padding: 15px;
  font-size: var(–fontsize);
}

@media screen and (min-width: 450px) {
  .container {
    –fontsize: 50px;
  }
   :root {
    –blue: lightblue;
  }
}

Try it Yourself »

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Browser Support

The numbers in the table specify the first browser version that fully supports the var() function.

Function
var()	49.0	15.0	31.0	9.1	36.0

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CSS var() Function

Property	Description
var()	Inserts the value of a CSS variable

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