<!DOCTYPE html>
<html lang="en-US">
<head>
<style>
body{
margin:0px !important;
}
div{
width:100vw;
background-color:#cccccc;
}
</style>
</head>
<body>
<div>
<p>width of this div is exact equal to the width of this frame.</p>
<p>Try to resize the width of this window. 'vw' will calculate the width automatically.</p>
<p>100vw is very similar to 100% only when body margin is equal to 0.</p>
</div> </body>
</html>