<!DOCTYPE html>
<html lang="en-US">
<head>
<style>
#parent{
display: flex;
width: 100%;
border: 1px solid #8c8c8c;
width:500px;
}
#parent > div{
border:1px solid #267326;
padding:25px 0;
text-align:center;
flex-basis: 100px;
-webkit-flex-basis: 100px;
}
</style>
</head>
<body>
<h1>CSS flex-basis Property</h1>
<div id="parent">
<div>Div 1</div>
<div>Div 2</div>
<div>Div 3</div>
</div>
<button onclick="myFunction()">Click Me</button>
<script>
var x = document.getElementById("parent").firstElementChild;
function myFunction(){
x.style.flexBasis = "200px";
x.style.WebkitFlexBasis = "200px";
}
</script>
<p><strong>Note</strong>: Click on the button to set the basic lenght of the 'div1' from 100px to 200px.</p> </body>
</html>