In today’s digital age, having a website that stands out from the rest is crucial to attract and retain visitors. CSS (Cascading Style Sheets) is an essential tool for creating visually appealing and user-friendly websites. And mastering CSS styling is a must-have skill for any web developer or designer. One of the most powerful features of CSS is the ability to use variables to create consistent themes across a website. This guide will take you through the basics of using CSS variables, including how to declare and use them, how to create reusable and maintainable code, and how to take advantage of their benefits for theming. By the end of this guide, you’ll be equipped with the knowledge and skills to use CSS variables to create beautiful and consistent themes across your website. So let’s dive in and start mastering CSS styling!

What are CSS variables?

CSS variables, also known as custom properties, provide a way to define values that can be reused throughout a CSS document. They were introduced in CSS3 and are now widely supported by modern browsers. With CSS variables, you can define values for properties such as colours, fonts, and sizes, and then reference them throughout your CSS code. This makes it easier to maintain consistency in your design and allows you to make global changes to your website’s styling by simply updating a variable. CSS variables are declared using the — prefix followed by a name and a value. For example, you might declare a variable for the primary colour of your website like this: :root {  –primary-color: #007bff;} Once you’ve declared a variable, you can reference it in other parts of your CSS code using the var() function. For example, you might use the primary colour variable to style a button like this: button {  background-color: var(–primary-color);  color: white;  padding: 10px 20px;  border: none;  border-radius: 5px;}

Benefits of using CSS variables for theming

Using CSS variables for theming has several benefits. First, it makes it easier to maintain consistency across your website. By defining variables for common values such as colours and fonts, you can ensure that they are used consistently throughout your design. This can help create a cohesive look and feel for your website, which can improve the user experience. Second, CSS variables make it easier to update your website’s styling. Because variables are defined in one place and referenced in multiple places, you can make global changes to your design by updating a variable. For example, if you decide to change the primary colour of your website, you can simply update the value of the primary colour variable, and all elements that reference that variable will be updated automatically. Finally, using CSS variables can help you write more maintainable code. By defining variables for commonly used values, you can avoid repeating the same values throughout your CSS code. This can make your code easier to read and understand, which can save time and reduce errors.

How to declare and use CSS variables

Declaring and using CSS variables is relatively simple. To declare a variable, you need to define it in the :root pseudo-class, which is used to define global styles for your document. For example, to define a variable for the primary colour of your website, you might use the following code: :root {  –primary-color: #007bff;} Once you’ve defined your variables, you can use them throughout your CSS code using the var() function. For example, to set the background colour of an element to the primary colour variable, you might use the following code: .element {  background-color: var(–primary-color);} You can also use CSS variables in other parts of your CSS code, such as font size, font family, and margin and padding values. For example: h1 {  font-size: var(–font-size-xl);  font-family: var(–font-family-heading);  margin-bottom: var(–spacing-lg);}

Creating a basic theme with CSS variables

Now that you know how to declare and use CSS variables, let’s create a basic theme using variables. First, we’ll define our variables in the :root pseudo-class. Here’s an example of how you might define variables for a basic theme: :root {  –primary-color: #007bff;  –secondary-color: #6c757d;  –font-family-body: ‘Helvetica Neue’, Helvetica, Arial, sans-serif;  –font-family-heading: ‘Helvetica Neue’, Helvetica, Arial, sans-serif;  –font-size-base: 16px;  –line-height-base: 1.5;  –spacing-xs: 4px;  –spacing-sm: 8px;  –spacing-md: 16px;  –spacing-lg: 32px;  –border-radius: 5px;} In this example, we’ve defined variables for the primary and secondary colours of our theme, as well as fonts, font sizes, line heights, spacing, and border radius. Once we’ve defined our variables, we can use them throughout our CSS code. Here’s an example of how we might use these variables to style a basic layout: body {  font-family: var(–font-family-body);  font-size: var(–font-size-base);  line-height: var(–line-height-base);  background-color: var(–secondary-color);  color: var(–primary-color);}.container {  max-width: 1200px;  margin: 0 auto;  padding: var(–spacing-md);}.header {  background-color: var(–primary-color);  color: white;  padding: var(–spacing-md);  border-radius: var(–border-radius);}h1, h2, h3, h4, h5, h6 {  font-family: var(–font-family-heading);  margin-bottom: var(–spacing-sm);}.btn {  background-color: var(–primary-color);  color: white;  padding: var(–spacing-sm) var(–spacing-md);  border: none;  border-radius: var(–border-radius);  cursor: pointer;}.btn:hover {  background-color: lighten(var(–primary-color), 5%);} In this example, we’ve used our variables to set font families, font sizes, line heights, background colours, text colours, spacing, and border radius. This creates a consistent look and feel for our website, which can improve the user experience.

Advanced theming techniques with CSS variables

In addition to basic theming, CSS variables can be used for more advanced theming techniques. For example, you can define variables for different states of an element, such as hover or active. This allows you to create more dynamic and interactive designs. Here’s an example of how you might define variables for the hover state of a button: .btn {  background-color: var(–primary-color);  color: white;  padding: var(–spacing-sm) var(–spacing-md);  border: none;  border-radius: var(–border-radius);  cursor: pointer;}.btn:hover {  background-color: var(–primary-color-hover);}:root {  –primary-color: #007bff;  –primary-color-hover: #0062cc;} In this example, we’ve defined a variable for the hover state of our button, which is a slightly darker shade of our primary colour. We’ve then referenced this variable in the :hover pseudo-class for our button. This creates a more dynamic and interactive design, which can improve the user experience.

Best practices for using CSS variables for theming

When using CSS variables for theming, there are several best practices you should follow:

1. Define your variables in the :root pseudo-class to ensure they are available for all elements.
2. Use meaningful variable names to make your code more readable and maintainable.
3. Define variables for commonly used values such as colours, fonts, and spacing to ensure consistency in your design.
4. Use variables in other parts of your CSS code, such as margin and padding values, to avoid repeating values throughout your code.
5. Consider using variables for different states of an element, such as hover or active, to create more dynamic and interactive designs.
6. Test your code across multiple browsers to ensure compatibility with older browsers that may not support CSS variables.

Tools and resources for working with CSS variables

There are several tools and resources available for working with CSS variables. Here are a few to get you started:

1. CSS Variables Playground https://codepen.io/jh3y/pen/VzEOPP – A CodePen playground that lets you experiment with CSS variables.
2. CSS Variables: Why Should You Care? https://www.smashingmagazine.com/2017/04/css-variables-theming-design-systems/ – A Smashing Magazine article that explains the benefits of using CSS variables for theming.
3. CSS Custom Properties for Cascading Variables https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties – The Mozilla Developer Network documentation for CSS variables.
4. Sass https://sass-lang.com/ – A preprocessor that extends CSS with variables, functions, and other features.

Examples of websites using CSS variables for theming

Many websites are now using CSS variables for theming. Here are a few examples:

1. GitHub https://github.com/ – GitHub uses CSS variables extensively for theming. Variables are used to define colours, fonts, and spacing throughout the site.
2. CodePen https://codepen.io/ – CodePen uses CSS variables to create a consistent look and feel across the site. Variables are used to define colours, fonts, and spacing, as well as for different states of elements such as hover and active.
3. Stripe https://stripe.com/ – Stripe uses CSS variables to create a consistent look and feel across the site. Variables are used to define colours, fonts, and spacing, as well as for different states of elements such as hover and active.

Conclusion

Using CSS variables for theming is a powerful technique that can help you create beautiful and consistent designs for your website. By defining variables for commonly used values such as colours, fonts, and spacing, you can ensure consistency in your design and make it easier to update your website’s styling. Additionally, by using variables for different states of elements, you can create more dynamic and interactive designs. Follow the best practices outlined in this guide, and explore the tools and resources available for working with CSS variables. With practice, you’ll become a master of CSS styling and be able to create stunning designs for your website.