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Nikolas Barwicki - Javascript Blog Nikolas's Blog

Amp Up Your CSS: Understanding and Using CSS Variables

/ 5 min read

Experienced developers are always looking for ways to improve their CSS skills and discover hidden gems within the language. One such treasure that can take your coding to the next level is CSS variables, also known as custom properties.

CSS variables are user-defined variables that store specific values to be reused throughout your CSS files. Using the syntax --variable-name: value;, you can declare variables within CSS selectors. Once you’ve assigned a value to a variable, you can use it anywhere in your stylesheets by invoking var(--variable-name).

Benefits of CSS Variables

CSS variables offer several benefits to developers:

1. Improved Code Maintenance - When you need to change a value that is used multiple times in your stylesheet, CSS variables make it much easier. Instead of manually locating each occurrence and adjusting it, you can simply update the value of the variable, automatically changing all other instances where the variable is used.

2. Increased Coding Efficiency - By centralizing values with CSS variables, you eliminate the need for repetition, resulting in DRY (Don’t Repeat Yourself) code. This not only speeds up coding but also improves site loading times and creates a more efficient codebase overall.

Using Global Variables for Streamlined Styling

Imagine a situation where you have to repeat the same font family, color, or margin across numerous CSS classes. With CSS global variables, you can simplify this process significantly.

To declare global variables, use the :root selector. For example:

:root {
  --main-font: Arial, sans-serif;
  --primary-color: #333;
  --gutter-width: 30px;

Once you’ve defined the variables, you can apply them using the var() function. Here’s an example that applies the global variables to the body of an HTML document:

body {
  font-family: var(--main-font);
  color: var(--primary-color);
  margin: var(--gutter-width);

The power of global variables lies in their ease of control. Need to switch to a new font or a different color theme? Simply update the variable. This level of flexibility makes CSS variables invaluable for keeping your CSS code DRY and manageable.

Providing Fallback Values for Robust Styling

To ensure your design remains functional even when CSS variables cannot be applied, it’s essential to provide fallback values. This is particularly important when working with older browsers that don’t support CSS variables.

To specify a fallback value, use the following syntax:

element {
  property: var(--your-variable, fallbackValue);

For example, if you want to set a fallback color for a theme but allow the user to define their own color preference, you can implement it like this:

.theme {
  background-color: var(--theme-color, blue);

By including a fallback value, you ensure that even if the variable is undefined, your design will still be functional.

Understanding the Cascade: Overriding Variables

CSS variables follow the cascading principle, allowing their values to be overridden in child elements. This flexibility enables you to define a global variable but set a different value for that variable on individual elements or sections of your page.

For example, suppose you have a global variable for text color set to black:

:root {
  --font-color: black;

body {
  color: var(--font-color);

If you want the text color to be different in a specific section of the page, you can redefine the variable within that section:

section {
  --font-color: blue;

This local redefinition won’t affect the rest of the page, allowing you to create highly adaptable styles with just a few variable value changes.

Enhancing Responsive Design with CSS Variables and Media Queries

The combination of CSS variables and media queries brings unparalleled versatility to responsive design. Media queries enable you to modify the design and layout of web pages based on device-specific rules, while CSS variables ensure consistency and dynamic scaling of styles across different elements.

For example, suppose you want your web elements to adjust their margin based on screen resolution. You can achieve this by setting a base margin using a CSS variable and integrating it with a media query:

:root {
  --base-margin: 10px;

div {
  margin: var(--base-margin);

@media (min-width: 600px) {
  :root {
    --base-margin: 20px;

By combining CSS variables and media queries, you can create highly responsive and adaptive designs that adapt to the environment.

Harnessing the Power of Calculations with CSS Variables

The calc function in CSS allows for dynamic calculation of property values, and CSS variables enhance its functionality even further. By storing specific values in variables and combining them with calc, you gain greater flexibility and efficiency in creating dynamic layouts.

For example, you can use CSS variables with calc to create a dynamic padding and margin layout:

:root {
  --padding: 10px;
  --margin: 20px;

.box {
  padding: calc(var(--padding) * 2);
  margin: calc(var(--margin) * 3);

By changing the values of the variables, you can easily adjust the padding and margin throughout your design, offering greater responsiveness and flexibility.

Maximizing Multiple Variables for One CSS Property

CSS variables allow you to use multiple variables to modify a single CSS property, providing increased flexibility in tweaking your design. The ability to update multiple variables for color schemes is a perfect example of this.

For example, instead of adjusting individual RGB values across multiple properties, you can use CSS variables to simplify the process. Here’s how:

:root {
  --red: 255;
  --green: 0;
  --blue: 0;

body {
  background-color: rgb(var(--red), var(--green), var(--blue));

By updating the values of the variables, you can easily change the entire color scheme of your web page without manually adjusting each property.

In Conclusion

CSS variables, or custom properties, offer a cleaner and more efficient way to style elements, making code maintenance a breeze. They provide flexibility and adaptability, allowing for global and local variables, fallback values, and the ability to override variables in child elements. Combining CSS variables with media queries, calculations, and multiple variables for a single property opens up a world of possibilities for scalable and responsive design.

As a developer, don’t be afraid to experiment and push the boundaries of what can be achieved with CSS variables. Incorporate these techniques into your workflow to streamline your development process, create modular and maintainable code, and ultimately deliver top-notch user interfaces. Happy coding!