CSS Variables: How to Use Them to Streamline Your Styling

CSS Variables, also known as custom properties, provide a powerful way to manage and reuse values throughout your stylesheets. They can make your code more maintainable, improve readability, and reduce repetition. In this blog post, we'll go over the basics of CSS Variables, show you how to declare and use them, explore their scope and inheritance, and discuss how to leverage them in responsive design and theming. We'll wrap up with a FAQ section to address some common questions. Let's dive in!

What are CSS Variables?

CSS Variables are custom properties that allow you to store values for reuse throughout your stylesheets. They can be applied to elements, classes, or even global styles, making them an incredibly flexible and powerful tool in your CSS toolkit. CSS Variables help reduce repetition, maintain consistency, and make it easier to update your styles across your entire project.

Declaring CSS Variables

To declare a CSS Variable, you'll use the following syntax:

--variable-name: value;

The variable name starts with two dashes (--) followed by the desired name, which can be any combination of letters, digits, hyphens, and underscores. The variable name is then followed by a colon and the value you'd like to store.

For example, let's declare a CSS Variable for a primary color:

--primary-color: #ff5733;

Global vs. Local Variables

CSS Variables can be declared globally or locally. Global variables are accessible throughout the entire stylesheet, while local variables are scoped to a specific element or selector.

Global Variables

To declare a global variable, add it to the :root pseudo-class:

:root {
  --primary-color: #ff5733;
  --secondary-color: #33c3ff;
}

Local Variables

To declare a local variable, add it to a specific selector:

.button {
  --button-bg-color: #ff5733;
}

This variable will only be available within the .button selector and its descendants.

Using CSS Variables

To use a CSS Variable, you'll use the var() function with the variable name as its argument:

element {
  property: var(--variable-name);
}

For example, let's use our previously declared --primary-color variable:

.header {
  background-color: var(--primary-color);
}

This will set the background color of the .header element to the value stored in --primary-color.

Fallback Values

You can provide a fallback value in case a variable is not defined:

element {
  property: var(--variable-name, fallback-value);
}

For example:

.header {
  background-color: var(--primary-color, #333);
}

If --primary-color is not defined, the background color will default to #333.

Scope and Inheritance

CSS Variables follow the same scoping and inheritance rules as other CSS properties.

Scope

A variable's scope is determined by where it's declared:

• Global variables are available throughout the entire stylesheet.
• Local variables are available within their selector and its descendants.

Inheritance

Variables are inherited from parent elements to their children, just like other CSS properties. If a child element doesn't have a value for a specific variable, it will inherit the value from its nearest ancestor that has it defined.

Responsive Design and CSS Variables

CSS Variables can be incredibly useful in responsive design, as they allow you to easily update values across multiple breakpoints.

For example, let's say you want to change the font size of your headings based on the screen width. You can do this with a combination ofCSS Variables and media queries:

:root {
  --heading-font-size: 2rem;
}

@media (min-width: 768px) {
  :root {
    --heading-font-size: 2.5rem;
  }
}

@media (min-width: 1024px) {
  :root {
    --heading-font-size: 3rem;
  }
}

h1, h2, h3, h4, h5, h6 {
  font-size: var(--heading-font-size);
}

In this example, we're defining a --heading-font-size variable and using it to set the font size for all headings. We then update the value of the variable based on different screen widths using media queries. As the screen width increases, the font size of the headings will also increase.

Theming with CSS Variables

One common use case for CSS Variables is implementing theming in your projects. By using variables for your colors, fonts, and other design elements, you can quickly and easily update the look and feel of your entire site.

For example, let's create a light and dark theme using CSS Variables:

:root {
  --bg-color: #ffffff;
  --text-color: #333333;
}

.dark-theme {
  --bg-color: #333333;
  --text-color: #ffffff;
}

body {
  background-color: var(--bg-color);
  color: var(--text-color);
}

Here, we define two themes: a light theme (the default) and a dark theme. We use the .dark-theme class to change the values of our color variables when applied to the body element. This allows us to easily switch between themes by toggling the .dark-theme class on the body.

FAQ

Can I use CSS Variables with preprocessors like Sass or Less?

Yes, you can use CSS Variables alongside preprocessors like Sass or Less. While preprocessors also have their own variable systems, CSS Variables offer some advantages, such as dynamic updates in the browser and the ability to inherit values.

What is the browser support for CSS Variables?

As of September 2021, CSS Variables are supported in all major modern browsers, including Chrome, Firefox, Safari, and Edge. Internet Explorer does not support CSS Variables. You can check the latest browser support information on Can I use.

Can I use JavaScript to manipulate CSS Variables?

Yes, you can use JavaScript to read and update the values of CSS Variables. To get the value of a CSS Variable, you can use the getComputedStyle() function:

const rootStyles = getComputedStyle(document.documentElement);
const primaryColor = rootStyles.getPropertyValue('--primary-color').trim();

To set the value of a CSS Variable, you can use the setProperty() method on the style property of an element:

document.documentElement.style.setProperty('--primary-color', '#ff0000');

This can be useful for creating dynamic themes, adjusting styles based on user preferences, or reacting to changes in your application's state.