Mastering CSS Variables: Pro Tips and Best Practices

Unlock the Power of CSS Variables

CSS offers a vast array of predefined standard key-value-based properties for styling semantic HTML elements. However, when designing web pages, developers often find themselves repeating the same values for properties across multiple segments of stylesheets. CSS now supports custom properties, also known as CSS variables, to alleviate this issue.

What are CSS Variables?

CSS variables allow you to declare a variable, assign it a value, and use it across your document. This feature enables you to write clean code with a productive assignment and retrieval syntax, scoping support, and fallback values. If you’re familiar with CSS preprocessors like Sass and Less, you’ll love the native support for variables in CSS.

How to Use CSS Variables

To declare a CSS variable, come up with a name, append two hyphens as the prefix, and assign a value. For example: --bg-color: #f2ba2c;. To access the variable, use the var() function and pass in the variable name: background-color: var(--bg-color);.

Inheritance and Cascading

CSS variables follow standard property rules, inheriting values from parent elements and adhering to the CSS specificity algorithm. You can also use CSS variables inheritance to pass variable values from parent elements to child elements without re-declaring them.

Fallback and Invalid Values

When using custom properties, you can specify a fallback value to be used in place of an undefined value. The syntax for providing a fallback value is still the var() function. For example: color: var(--light-gray, #f0f0f0);.

Creating Scoped CSS Variables

By default, browsers won’t scope style tags even if you wrap them with elements like <div> for creating scoped variables. The @scope at-rule helps implement scoped CSS variables with scoped style tags.

Four Projects to Get You Started

We’ll build four simple projects to demonstrate the power of CSS variables:

1. Button Variations: Create a base design across elements using CSS variables.
2. Theme-Based Design: Build a light-and-dark theme manipulated by JavaScript.
3. Responsive Login Form: Display different layouts on desktop, tablet, and mobile screens using CSS variables and media queries.
4. JavaScript-Free Dynamic Elements: Generate a colorful native checkbox list using CSS variables and the hsl color function.

Browser Support

According to the browser compatibility table, the CSS variables feature is widely available in all popular browser versions released after April 2017.

Take Your Frontend to the Next Level

By mastering CSS variables, you can simplify your code, improve maintainability, and create complex animations with ease. Try LogRocket to monitor and track client-side CPU usage, memory usage, and more for all of your users in production.