How to change CSS styles using JS?

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JavaScript is often used to change the CSS properties of a webpage dynamically. It allows web developers to manipulate the style and layout of a webpage in real time based on user interaction or other events.

Change CSS styles using JS

There are several reasons for the usage of JavaScript for this purpose:

  1. Interactivity: By using JavaScript to change the CSS of a webpage, developers can create more interactive and engaging user experiences. For example, hovering over an element could cause its color to change or a tooltip to appear.
  2. Responsiveness: By adjusting its layout and style, JavaScript can make a webpage more responsive. It can respond to changes in the viewport size or device orientation.
  3. Dynamic content: JavaScript creates a dynamic range generated based on user input or other events. For example, a form might update its appearance based on the user’s selections, or a slideshow might change its images automatically. 
  4. Animation: JavaScript can create animations on a webpage by manipulating CSS properties over time. You can use this to create engaging visual effects. Such as fading in and out, sliding in and out, or scrolling.

See Also: Top 7 Hands-On HTML CSS Projects For Beginners To Practice

Process of changing CSS using JS

The process of changing CSS through JavaScript involves the following steps:

1. Select the HTML element that you want to modify

  • You can use techniques like ‘getElementById,’ ‘querySelector,’ or ‘getElementsByClassName’ to select the element based on its class, tag name, or ID.

2. Access the ‘style’ property of the selected element

  • The ‘style’ property allows you to modify the CSS properties of the selected element.

3. Modify the CSS properties using JavaScript

  • You can modify CSS properties by assigning new values to the corresponding properties of the ‘style‘ object. For example, to change the background color of an element, you can assign a new color value to the ‘backgroundColor’ property of the ‘style’ object.

4. Save the changes by applying the modified CSS to the element

  • The changes will only work properly once the user applies them to the designated element. You can do this by assigning the modified element back to the original HTML element or by using the ‘setAttribute’ method to alter the element’s inline style.

Here’s an example of how you can change the CSS properties of an HTML element using JavaScript:

Change CSS properties of html

In this example, we select the ‘div’ element with the ID ‘”myDiv,”‘ and then we modify its background color and text color and add a CSS class called ” highlight.”‘ When the ‘changeCSS‘ function is called by clicking the button, the changes take effect on the selected element.

Change CSS styles using JS

To change CSS styles using JS, you can use the style property of the HTML element you want to modify.

  • For example, you can apply the following code if you wish to change the color of a ‘div’ element:

Change the color

This code gets the ‘div’ element with the ‘id’ of ‘”myDiv”‘ using the ‘getElementById‘ method and assigns it to the ‘div’ variable. Then, it changes the ‘color’ property of the ‘style’ object of the ‘div’ element to ‘”red.”‘

  • You can also change other CSS properties, such as ‘backgroundColor,’ ‘fontSize,’ and ‘fontWeight,’ etc., by modifying the corresponding properties of the ‘style’ object.

Background color

  • You can also work with JavaScript to add or pull-out CSS classes from an element. It can change multiple styles at once.

Change Multiple styles

In this example, the add method adds a CSS class called ‘”highlight”‘ to the ‘div’ element, which can be defined in a stylesheet. The ‘remove’ method removes the ‘”highlight”‘ class from the ‘div’ element.

  • To change CSS styles using JavaScript, you can manipulate the ‘style’ property of the HTML element you want to modify. Here’s an example of how to do it:





This code selects the ‘div’ element with the ‘id’ of ‘”myDiv”‘ using the ‘getElementById’ method and assigns it to the ‘div’ variable. Then, it changes the background color of the ‘div’ element to ‘”blue”‘ by modifying the ‘backgroundColor’ property of the ‘style’ object of the ‘div’ element. It also changes the font size to ‘”24px”‘ and font weight to ‘”bold”‘ by modifying the ‘fontSize’ and ‘fontWeight’ properties, respectively.

  • You can also modify multiple styles at once by chaining the style properties together:

Modify Together

In this example, the ‘cssText’ property sets the CSS styles of the ‘div’ element all at once, using a CSS-like syntax. Semicolons separate the properties and their values; the entire string is enclosed in quotes.

See Also: How To Display Time In HTML Using JavaScript?


In summary, JavaScript is often used to change CSS.  It allows web developers to create more interactive, responsive, and dynamic user experiences, animations, and visual effects.

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