Webmastertoolbag Tryit Editor

<!DOCTYPE html>
<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="none">
  
  
</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>
    
    <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>