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<!DOCTYPE html>
<html>
<head>
<style> 
#main {
  width: 220px;
  height: 300px;
  border: 1px solid black;
  display: flex;
  align-items: flex-start;
}
#main div {
  flex: 1;
}
#myBlueDiv {
  align-self: center;
}
</style>
</head>
<body>
<h1>Change align-self with JavaScript</h1>
<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 with more content.</div>
</div>
<p>Click the "Try it" button to set the value of the alignSelf property to "stretch"</p>
<button onclick="myFunction()">Try it</button>
<script>
function myFunction() {
  document.getElementById("myBlueDiv").style.alignSelf = "stretch";
}
</script>