Using CSS variables and custom properties

Comprehensive Guide to Using CSS Variables and Custom Properties in Web Development

As a web developer, you’re always seeking ways to streamline your workflow and enhance the functionality and maintainability of your projects. One of the most powerful features brought into the world of CSS is CSS Variables, also known as custom properties. This guide will take you through the essentials of CSS Variables, helping you to understand how to effectively implement them in your web projects, and illustrating the benefits they can bring.

What are CSS Variables?

CSS Variables, officially known as Custom Properties, are entities defined by CSS authors that contain specific values to be reused throughout a document. They follow the format --example-name: value; and can be used in other CSS properties using the var() function.

Why Use CSS Variables?

Maintainability: Changes need to be made only at the variable definition, rather than everywhere the value is used.
Readability: Names given to custom properties can be more descriptive about their usage.
Reusability: Helps in building a consistent theming system across a site.
Dynamic Manipulation: CSS Variables can be manipulated in real-time through JavaScript, a very useful feature particularly for theming and adjusting layouts dynamically.

Defining and Using CSS Variables

You can define CSS Variables inside any selector, but they're commonly defined inside the :root selector which makes them global and accessible throughout the entire stylesheet.

:root {
  --primary-color: #292b2c;
  --secondary-color: #484848;
  --padding: 10px;
}

To use a variable, you employ the var() function. Here’s how you can use the variables defined above:

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

.container {
  padding: var(--padding);
}

Scope and Cascading

Variables in CSS obey the cascading rules of CSS. This means if you redefine a variable inside a particular selector, it will override the global definition within that specific scope.

.special-text {
  --primary-color: #ff4500;  /* Redefining within a selector */
  color: var(--primary-color);  /* This will now be orange */
}

Compatibility and Fallback

While most modern browsers support CSS Variables, it’s a good practice to include a fallback for older browsers. This can be done by placing the fallback value right before the variable in var().

.container {
  background-color: white;  /* Fallback for older browsers */
  background-color: var(--primary-color, white);  /* Modern browsers will use this */
}

Dynamic Control with JavaScript

One of the most powerful features of CSS Variables is their real-time controllability through JavaScript, enabling dynamic changes without reloading the page.

document.documentElement.style.setProperty('--primary-color', '#000000');

Practical Examples

Responsive Design

You can define variables for different breakpoints which then can easily be applied within other rulesets.

:root {
  --text-size: 16px;
}

@media (max-width: 768px) {
  :root {
    --text-size: 14px;
  }
}

.body {
  font-size: var(--text-size);
}

Theme Swapping

Swapping themes dynamically is straightforward with CSS Variables and JavaScript.

.light-theme {
  --background-color: #fff;
  --font-color: #000;
}

.dark-theme {
  --background-color: #333;
  --font-color: #ddd;
}

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

Components Theming

CSS Variables provide a straightforward way to style components consistently.

.button {
  background-color: var(--btn-background, blue);
  color: var(--btn-color, white);
}

Conclusion

CSS Variables offer incredible power to web developers looking to create dynamic, maintainable, and scalable stylesheets. Their integration with JavaScript and the ability to cascade and scope them wisely can revolutionize how we approach CSS today. Any web developer, whether beginner or advanced, should take advantage of this powerful feature in modern web development.

Start incorporating CSS Variables into your workflows and enjoy the flexibility and control they bring to your design. Happy coding!