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<!DOCTYPE html>
<html>
<head>
<style>
#myDIV {
 width: 500px;
 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% {max-height: 100px;}
}

/* Standard syntax */
@keyframes mymove {
 50% {max-height: 100px;}
}
</style>
</head>
<body>

Change the max-height, from "none" to "100px" and back to "none":

<div id="myDIV">
 This DIV element does not have a pre-defined height.
 An animation will change the max-height, from "none" to "100px".
 The height of this DIV element will not exceed 100 pixels.
</div>

The max-height property is animatable in CSS.
Note: Currently the max-height property is not changing gradually in Chrome, and does not change at all in Firefox.
Note: CSS Animations do not work in Internet Explorer 9 and earlier versions.

</body>
</html>

<!DOCTYPE html>
<html>
<head>
<style> 
#myDIV {
    width: 500px;
    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% {max-height: 100px;}
}

/* Standard syntax */
@keyframes mymove {
    50% {max-height: 100px;}
}
</style>
</head>
<body>

<p>Change the max-height, from "none" to "100px" and back to "none":<p>

<div id="myDIV">
  <p>This DIV element does not have a pre-defined height.</p>
  <p>An animation will change the max-height, from "none" to "100px".</p>
  <p>The height of this DIV element will not exceed 100 pixels.</p>
</div>

<p>The max-height property is <em>animatable</em> in CSS.</p>
<p><b>Note:</b> Currently the max-height property is not changing <em>gradually</em> in Chrome, and does not change at all in Firefox.</p>
<p><b>Note:</b> CSS Animations do not work in Internet Explorer 9 and earlier versions.</p>

</body>
</html>