<html lang="en"><head> <title>Bootstrap Example</title> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css"> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script></head><body><div class="container-fluid"> <h1>Hello World!</h1> <div class="row"> <div class="col-xs-6 col-sm-3" style="background-color:lavender;"> Column 1<br> Resize the browser window to see the effect. Also try to remove the div clearfix line and see what happens. </div> <div class="col-xs-6 col-sm-3" style="background-color:lavenderblush;">Column 2</div> <!-- Add clearfix for only the required viewport --> <div class="clearfix visible-xs"></div> <div class="col-xs-6 col-sm-3" style="background-color:lightcyan;">Column 3</div> <div class="col-xs-6 col-sm-3" style="background-color:lightgray;">Column 4</div> </div></div></body>