CSS custom properties, also known as CSS variables, were introduced in CSS3 as a way to make it easier to reuse and maintain styling across a website. With CSS custom properties, you can define a value once and use it throughout your stylesheet, making it easier to make global changes to your website’s design without having to edit multiple places. In this article, we’ll explore how to use CSS custom properties and some of the benefits they provide.

To create a custom property, you simply define it with a double hyphen prefix, followed by a name and a value:

:root {
    --primary-color: #0088cc;
}

In this example, we’ve defined a variable named “--primary-color” and given it a value of “#0088cc“. We’ve placed this definition in the :root selector to make it global to the entire document.

Once you’ve defined a custom property, you can use it throughout your stylesheet by referencing its name with the var() function:

a {
    color: var(--primary-color);
}

In this example, we’re setting the color of all anchor tags to the value of our custom property, “--primary-color“. This makes it easy to change the color of all links on our website by simply changing the value of the custom property. You can also use this same variable to color other highlighted elements like buttons, borders, and backgrounds.

One of the key benefits of CSS custom properties is that they make it easier to maintain a consistent design across your website. By defining global values in custom properties, you can make sure that your colors, fonts, and other design elements are consistent across all pages.

Custom properties can also make it easier to create responsive designs. Let’s say you have a navigation menu on your website that collapses into a hamburger menu on smaller screens. You want to change the background color of the navigation menu when it’s in its collapsed state to make it more visible. You can use CSS variables to define the background color for different screen sizes.

First, define a custom property for the background color:

--menu-bg-color: #ffffff;

Next, use media queries to change the value of the custom property for different screen sizes:

@media screen and (max-width: 768px) {
    :root {
        --menu-bg-color: #333333;
    }
}

Finally, use the custom property to style the navigation menu:

.nav-menu {
    background-color: var(--menu-bg-color);
}

In this example, the background color of the navigation menu will be white by default, but will change to dark gray when the screen width is 768px or less. This makes the menu more visible and easier to use on smaller screens. By using CSS custom properties and media queries, you can create responsive designs that adapt to different screen sizes and provide a better user experience.

In addition to making it easier to maintain a consistent design and create responsive layouts, CSS custom properties can also help reduce the size of your stylesheets. By using custom properties to define global values, you can avoid repeating the same values throughout your stylesheet, which can help reduce the file size and make your site faster. This is especially beneficial when using long values like gradients and clip paths.

Here’s an example where CSS variables can save a considerable amount of time and file size. Instead of defining your font families on each element, you can define custom properties for each style:

--title-font: Impact, 'Helvetica Neue Condensed', 'Arial Narrow', sans-serif;
--body-font: Helvetica, Tahoma, Arial, sans-serif;

Now you can use the title font variable to style each of your headings, and the body font property to style your paragraphs and list items.

So, instead of entering a long list of font families dozens of times throughout your document, you can define one list to be used any number of times throughout your document. Any time you decide to change your title font or body font, you only have to enter it once.

CSS custom properties can be used to save values for any property, from simple margins, to binary images. They can also be used to store complex values, such as the results of CSS calculations. Here’s an example of using the calc() function in a variable:

--box-width: calc(100vw - 20px);

This custom property can then be used to set the width of any element:

.box {
    width: var(--box-width);
}

This would set the width of all .box elements to 20 pixels smaller than the width of the viewport.

Here are some additional tips and techniques for using CSS custom properties:

• Use descriptive names. This will make your code more readable and easier to understand down the road.
• Use consistent naming conventions. This will help you to keep track of your custom properties and make it easier to find them when you need them.
• Group related variables together. This will help to keep your code organized and easier to read.
• Use custom properties to store complex values. This can be useful for things like storing the results of calculations or storing data that needs to be reused throughout a stylesheet.
• Combine with other CSS features. CSS custom properties can be used in conjunction with other advanced CSS features such as calc(), media queries, and animations to create complex and dynamic designs.
• Use custom properties to create accessible designs. You can use custom properties to store values that can be used to make your designs more accessible, such as the color of text or the contrast between text and background. This can help people with disabilities to use your website more easily.
• Use fallback values. CSS custom properties can be nested, so it’s possible to set a fallback value for a property in case the browser doesn’t support custom properties. This ensures that the website will still be functional and styled even on browsers that don’t support CSS custom properties.

CSS custom properties are a hugely powerful new web technology that changes the game for web designers. They make it easier to create consistent designs and responsive layouts, as well as reducing the size of your stylesheets. By using custom properties to define global values, you can make it easier to maintain and update your website’s design, saving you time and effort in the long run.