Try it Editor: Animation of width

Edit This Code :

<!DOCTYPE html>
<html>
<head>
<style> 
#myDIV {
    width: 120px;
    background-color: coral;
    color: white;
    -webkit-animation: mymove 5s infinite; /* Chrome, Safari, Opera */
    animation: mymove 5s infinite;
}

/* Chrome, Safari, Opera */
@-webkit-keyframes mymove {
    50% {width: 500px;}
}

/* Standard syntax */
@keyframes mymove {
    50% {width: 500px;}
}
</style>
</head>
<body>

<h1>Animation of width</h1>

<p>Gradually change the width of the DIV element from 120px to 500px, and back to 120px:<p>

<div id="myDIV">
  <h1>My DIV</h1>
</div>

<p><strong>Note:</strong> CSS Animations do not work in Internet Explorer 9 and earlier versions.</p>

</body>
</html>
Result :