<style> #test1 { box-sizing: content-box; width: 300px; height: 100px; padding: 30px; border: 4px solid #c00;} #test2 { box-sizing: border-box; width: 300px; height: 100px; padding: 30px; border: 4px solid #008000;} </style> <div id="test1">box-sizing: content-box</div> <br><br> <div id="test2">box-sizing: border-box</div>