Custom Properties vs. CSS Variables: Understanding the Differences and When to Use Each

Ever found yourself repeating the same color value or font size throughout your CSS code? Managing these repetitive values can become cumbersome and hinder maintainability. This is where custom properties, also known as CSS variables, come in handy. They allow you to define reusable values within your stylesheets, promoting cleaner and more efficient CSS.

What are Custom Properties?

Custom properties are essentially variables you can define in your CSS to store specific values. These values can then be referenced throughout your stylesheet using the var() function. Here's the syntax for defining a custom property:

/* Define the custom property with a double hyphen (--) prefix */
--primary-color: blue;

/* Access the property value using var() */
h1 {
  color: var(--primary-color);
}

In this example, we define a custom property named --primary-color with the value blue. We can then use var(--primary-color) wherever we need to use the blue color, making it easy to update the color scheme across the entire website by simply changing the value of the custom property.

Custom Properties are Just Another Name for CSS Variables?

Yes, exactly! The terms "custom properties" and "CSS variables" are interchangeable. Both refer to the same functionality of storing and reusing values within CSS.

Key Differences and Use Cases

While custom properties offer a powerful way to manage reusable values, there are a few key aspects to consider:

Scope: Custom properties inherit their values by default. This means if you define a custom property at the root level (:root), its value will cascade down to all descendant elements unless overridden by a more specific declaration. This cascading nature makes them ideal for setting global styles or defining theme-based colors.
For example:

:root {
  --background-color: #f5f5f5;
}

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

.special-section {
  background-color: white; /* Overrides the inherited value */
}

In this example, the --background-color property sets the default background color for the entire website. However, the .special-section class overrides the inherited value with white.

Definition Location
Custom properties can be defined anywhere in your CSS code. However, some preprocessors like Sass or LESS offer more control over variable declaration and scoping.
When to Use Custom Properties

Custom properties shine in situations where:

You want to define global or theme-based styles that can be easily reused throughout the website.
Cascading behavior is desired, where child elements inherit the value unless explicitly overridden.

When Alternatives Might Be Better

For complex projects with intricate variable management needs and functionalities beyond basic re-use, preprocessors like Sass or LESS can be a better choice. These tools provide additional functionalities like nesting, mixins, and operations on variables, offering a more robust solution for complex stylesheets.

Conclusion

Custom properties (or CSS variables) are a valuable addition to your CSS toolkit. They promote cleaner and more maintainable code by eliminating repetitive value declarations. By understanding their scope, definition flexibility, and ideal use cases, you can effectively leverage them to create consistent and adaptable styles for your web projects. Remember, for highly complex projects with advanced variable management requirements, preprocessors can offer a more comprehensive solution.