What are CSS Transitions?

With the transition effect, you can easily change the property values. You can also set a duration.

Let us try to change the height of an element:


Live Demo

<!DOCTYPE html>
         div {
            width: 150px;
            height: 150px;
            background: blue;
            transition: width 3s;
         div:hover {
            height: 200px;
      <h1>Heading One</h1>
      <p>Hover over the below box to change its height.</p>