Try it Editor: Box-sizing

Edit This Code :


<!DOCTYPE html>
<html>
<head>
<style> 
div.container {
    width: 100%;
    border: 2px solid black;
}

div.box {
    box-sizing: border-box;
    width: 50%;
    border: 5px solid red;
    float: left;
}
</style>
</head>
<body>

<div class="container">
  <div class="box">This div occupies the left half</div>
  <div class="box">This div occupies the right half</div>
  <div style="clear:both;"></div>
</div>

</body>
</html>

Result :