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<!DOCTYPE html>
<html>
<head>
<style> 
#main {
  width: 250px;
  height: 100px;
  border: 1px solid #c3c3c3;
  display: flex;
}
#main div {
  flex-grow: 0;
  flex-shrink: 0;
  flex-basis: 50px;
}
#myBlueDiv {
  animation: mymove 5s infinite;
}
@keyframes mymove {
  50% {flex-basis: 200px;}
}
</style>
</head>
<body>
<h1>Animation of flex-basis</h1>
<p>Gradually change the flex-basis property of the BLUE div from 50px to 200px, and back:<p>
<div id="main">
  <div style="background-color:coral;">RED</div>
  <div style="background-color:lightblue;" id="myBlueDiv">BLUE</div>
</div>
</body>
</html>