CSS variables, also known as custom properties, are a powerful tool for simplifying and streamlining your CSS. They allow you to store values that can be reused throughout your stylesheet, making it easier to maintain and update your styles. In this chapter, we will cover how to use CSS variables and the benefits they provide.
Defining CSS Variables
CSS variables are defined using the --
prefix, followed by the variable name. The value of the variable is assigned using the :
symbol. CSS variables can be defined anywhere in your stylesheet, but it is generally best practice to define them at the top of your stylesheet or in a separate file.
For example, to define a variable for the primary color of your website, you could use the following CSS:
:root {
--primary-color: #0074D9;
}
This will create a variable called --primary-color
with a value of #0074D9
, which is a blue color.
Using CSS Variables
To use a CSS variable, you simply reference it using the var()
function. The var()
function takes the variable name as its first argument, and an optional fallback value as the second argument.
For example, to use the --primary-color
variable defined above as the color for all a
elements, you could use the following CSS:
a {
color: var(--primary-color);
}
This will set the color of all a
elements to the value of the --primary-color
variable. If the --primary-color
variable is not defined, the fallback value of #0074D9
will be used.
Benefits of Using CSS Variables
There are several benefits to using CSS variables:
- Simplify and streamline your CSS: CSS variables allow you to store values that can be reused throughout your stylesheet, reducing the need for repetitive and redundant code.
- Make updating your styles easier: By storing values in variables, you can easily update your styles by changing the value of the variable. This is especially useful for global values, such as colors or font sizes.
- Improve maintainability: CSS variables make it easier to maintain and update your styles, as you only need to change the value of the variable rather than searching for and updating the value throughout your stylesheet.
Tips for Using CSS Variables
- Define CSS variables at the top of your stylesheet or in a separate file for easy reference.
- Use descriptive and intuitive names for your variables to improve readability and maintainability.
- Use the
var()
function to reference CSS variables in your styles. - Use fallback values in the
var()
function to ensure that your styles are consistent if a variable is not defined.
Conclusion
CSS variables are a powerful tool for simplifying and streamlining your CSS. By defining and using variables, you can improve the maintainability and updateability of your styles. By following best practices and using descriptive and intuitive variable names, you can take full advantage of the benefits that CSS variables provide.
Exercises
To review these concepts, we will go through a series of exercises designed to test your understanding and apply what you have learned.
Write a CSS rule to define a variable called --main-font-size
with a value of 16px
. Then, use the --main-font-size
variable to set the font size of all h1
elements to 1.5em
.
:root {
--main-font-size: 16px;
}
h1 {
font-size: 1.5em;
}
Write a CSS rule to define a variable called --secondary-color
with a value of #FF851B
. Then, use the --secondary-color
variable to set the background color of all button
elements to #FF851B
.
:root {
--secondary-color: #FF851B;
}
button {
background-color: var(--secondary-color);
}
Write a CSS rule to define a variable called --border-radius
with a value of 5px
. Then, use the --border-radius
variable to set the border radius of all input
elements to 5px
.
:root {
--border-radius: 5px;
}
input {
border-radius: var(--border-radius);
}
Write a CSS rule to define a variable called --box-shadow
with a value of 0 5px 10px rgba(0, 0, 0, 0.2)
. Then, use the --box-shadow
variable to set the box shadow of all div
elements to 0 5px 10px rgba(0, 0, 0, 0.2)
.
:root {
--box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
}
div {
box-shadow: var(--box-shadow);
}
Write a CSS rule to define a variable called --main-font-family
with a value of Arial, sans-serif
. Then, use the --main-font-family
variable to set the font family of all p
elements to Arial, sans-serif
.
:root {
--main-font-family: Arial, sans-serif;
}
p {
font-family: var(--main-font-family);
}