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Dynamically Changing CSS Variables with JavaScript


CSS variables, also known as CSS custom properties, are a powerful feature introduced in CSS3 that allow developers to define reusable values and use them throughout their CSS code. These variables provide flexibility and maintainability by enabling the separation of style and content.

Dynamic styling refers to the ability to modify CSS styles on the fly, in response to user interactions or other events. This feature is essential for creating interactive and engaging user interfaces. However, static CSS styles alone are not sufficient for achieving dynamic styling effects. This is where dynamically changing CSS variables with JavaScript comes into play.

By using JavaScript, we can access and modify CSS variables programmatically, making it possible to dynamically change the styling of elements in real-time. This opens up a world of possibilities for creating custom styling effects and enhancing the user experience.

In the next sections, we will explore different methods of using JavaScript to modify CSS variables and demonstrate how to update CSS variables on the fly. We will also discuss the impact of dynamic styling on user experience and provide best practices for using dynamic styling with CSS variables.

Using JavaScript to Modify CSS Variables

JavaScript can be used to dynamically manipulate CSS variables, allowing for flexible and responsive styling on web pages. By accessing and modifying CSS variables with JavaScript, developers can create dynamic and interactive user experiences.

There are several methods for accessing and modifying CSS variables with JavaScript:

  1. Using This method allows you to directly set or change the value of a CSS variable. By specifying the variable name and the new value, you can dynamically update the styling of an element or a set of elements.'--primary-color', 'red');
  1. Using getComputedStyle(): This method retrieves the computed value of a CSS variable. By using getComputedStyle(element).getPropertyValue(), you can access the current value of a CSS variable and use it in your JavaScript code.
const primaryColor = getComputedStyle(document.documentElement).getPropertyValue('--primary-color');
  1. Using CSSOM: The CSS Object Model (CSSOM) allows you to access and modify CSS properties and values programmatically. By using the style property of an element, you can directly modify the value of a CSS variable.
const element = document.getElementById('myElement');'--primary-color', 'blue');

By utilizing these methods, developers can easily manipulate CSS variables with JavaScript to create dynamic and responsive styles on their web pages. Whether it's changing colors, fonts, or other visual properties, JavaScript provides the flexibility to modify CSS variables on the fly.

Updating CSS Variables on the Fly

To dynamically update CSS variable values, follow these steps:

  1. Access the CSS variable you want to update using the getComputedStyle() method.
  2. Modify the variable value using JavaScript by selecting the desired element and using the setProperty() method.
  3. Assign the modified value to the CSS variable using the setProperty() method again.

Here's an example:

// Step 1: Access the CSS variable
const root = document.documentElement;
const currentColor = getComputedStyle(root).getPropertyValue('--main-color');

// Step 2: Modify the variable value'--main-color', 'red');

// Step 3: Assign the modified value'--main-color', currentColor);

To trigger changes in CSS variables based on user actions, you can use event listeners. For example, you can add an event listener to a button click and update the CSS variable value accordingly.

const button = document.querySelector('button');

button.addEventListener('click', () => {
  // Update CSS variable value'--main-color', 'blue');

By updating CSS variables on the fly, you can achieve dynamic styling effects. For instance, you can change the background color of an element when the user hovers over it.

.element {
  background-color: var(--main-color);
  transition: background-color 0.3s ease;

.element:hover {
  background-color: var(--hover-color);
const element = document.querySelector('.element');

element.addEventListener('mouseenter', () => {
  // Update CSS variable value'--hover-color', 'yellow');

element.addEventListener('mouseleave', () => {
  // Update CSS variable value'--hover-color', 'green');

In this example, the background color of the element will change to yellow when the user hovers over it, and it will change to green when the user moves the mouse away.

By dynamically updating CSS variables, you can create interactive and engaging user experiences.

Enhancing User Experience with Dynamic Styling

Dynamically changing CSS variables can greatly enhance the user experience on a website or web application. By updating CSS variables on the fly, we can create dynamic styling effects that respond to user interactions and provide a more engaging and interactive interface.

One of the key benefits of dynamically changing CSS variables is the ability to create personalized experiences for users. By allowing users to customize certain elements of the design, such as colors or font sizes, we can make the website feel more tailored to their preferences. This level of personalization can increase user satisfaction and engagement.

For example, consider a website that allows users to change the background color. By updating the CSS variable that controls the background color based on the user's selection, we can instantly change the appearance of the entire website to match their preference. This not only provides users with a more visually appealing experience but also gives them a sense of ownership and control over the design.

Dynamic styling can also be used to enhance user interaction and engagement. By updating CSS variables in response to user actions, we can create visual feedback that guides users and provides a more intuitive experience. For instance, changing the color or opacity of a button when it is hovered over or clicked can give users a clear indication of their current interaction state.

Another example is using dynamic styling to create animations or transitions. By updating CSS variables that control animation properties, such as duration or easing, we can create smooth and visually pleasing effects that capture user attention and make the website feel more dynamic.

When using dynamic styling with CSS variables, it is important to follow best practices and consider some key considerations. Here are a few tips to keep in mind:

  1. Use descriptive variable names: Choose variable names that accurately reflect their purpose and usage. This will make it easier to understand and maintain the code.

  2. Limit the number of variables: While CSS variables provide flexibility, having too many variables can make the code harder to manage. Try to keep the number of variables to a minimum and consolidate where possible.

  3. Update variables efficiently: Dynamically changing CSS variables can have performance implications, especially if the changes trigger reflows or repaints. To optimize performance, batch multiple variable updates together and use techniques like debouncing or throttling.

  4. Test for cross-browser compatibility: CSS variables are supported in modern browsers, but it's important to test your code across different browsers to ensure compatibility. Consider using fallback values or polyfills for older browsers that do not support CSS variables.

By following these best practices and considering the impact on user experience, we can leverage the power of dynamic styling with CSS variables to create more engaging and interactive websites.


In conclusion, using JavaScript to dynamically change CSS variables provides several benefits. By allowing us to modify variable values on the fly, we can create dynamic and interactive web experiences for users.

Recapping the benefits, dynamically changing CSS variables with JavaScript enables us to easily update styles without modifying the underlying CSS code. This flexibility saves time and effort in making design changes, especially in large projects where updating individual styles can be cumbersome.

Furthermore, dynamic styling with CSS variables enhances the user experience by allowing for interactive and engaging elements on web pages. By updating variable values based on user actions, we can create visual effects, animations, and transitions that respond in real time. This level of interactivity can greatly improve user interaction and engagement.

In conclusion, leveraging JavaScript to modify CSS variables dynamically is a powerful technique that empowers web developers to create dynamic and responsive web designs. By embracing dynamic styling, we can enhance the user experience and create more interactive and engaging web applications.