<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script> <script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <!------ Include the above in your HEAD tag ----------> <div class="scale"> Scale </div> <div class="content-box"> Content Box </div> <div class="border-box"> Border Box </div>

div { width: 160px; height: 80px; padding: 20px; border: 8px solid red; background: yellow; } .content-box { box-sizing: content-box; border: 8px solid skyblue; width: 160px; padding: 20px; /* Total width: 160px + (2 * 20px) + (2 * 8px) = 216px Total height: 80px + (2 * 20px) + (2 * 8px) = 136px Content box width: 160px Content box height: 80px */ } .border-box { box-sizing: border-box; border: 8px solid blue; width: 160px; padding: 20px; /* Total width: 160px Total height: 80px Content box width: 160px - (2 * 20px) - (2 * 8px) = 104px Content box height: 80px - (2 * 20px) - (2 * 8px) = 24px */ }