Try it Yourself - CSS Reference anim

<!DOCTYPE html>
<html>
<head>
<style>
#myDIV {
   width: 50%;
   background-color: lightblue;
   overflow: auto;
   border: 1px solid black;
   -webkit-animation: mymove 5s infinite; /* Chrome, Safari, Opera */
   animation: mymove 5s infinite;
}

/* Chrome, Safari, Opera */
@-webkit-keyframes mymove {
   50% {min-width: 800px;}
}

/* Standard syntax */
@keyframes mymove {
   50% {min-width: 800px;}
}
</style>
</head>
<body>

<p>Change the min-width, from "none" to 800px and back to "none":<p>
<p><strong>Note:</strong> The min-width property overrides the width property.</p>

<div id="myDIV">
  <p>This DIV element has a pre-defined width: 50%.</p>
  <p>An animation will gradually change the min-width to 800 pixels.</p>
</div>

<p>The min-width property is <em>animatable</em> in CSS.</p>
<p><b>Note:</b> CSS Animations do not work in Internet Explorer 9 and earlier versions.</p>

</body>
</html>