​x
 
<!DOCTYPE html>
<html>
<head>
<style> 
#main {
  width: 270px;
  height: 300px;
  border: 1px solid black;
  display: flex;
}
​
#main div {
  -ms-flex: 1;  /* IE 10 */  
  flex: 1;
}
​
#myBlueDiv {
  animation: mymove 5s infinite;
}
​
@keyframes mymove {
  50% {flex: 3;}
}
</style>
</head>
<body>
​
<h1>flex 的动画效果：</h1>
​
<p>Gradually change the flex property of the BLUE div element from 1 to 3, and back:<p>
​
<div id="main">
  <div style="background-color:coral;">RED</div>
  <div style="background-color:lightblue;" id="myBlueDiv">BLUE</div>  
  <div style="background-color:lightgreen;">GREEN</div>
</div>
​
<p><b>注释：</b> Internet Explorer 10 supports an alternate, the -ms-flex property. IE11 and newer versions fully support the flex property (do not need the -ms- prefix).</p>
​
</body>
</html>
​