<!DOCTYPE html> <html> <head> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <style> * { box-sizing: border-box; } .left { background-color: #2196F3; padding: 20px; float: left; width: 20%; /* The width is 20%, by default */ } .main { background-color: #f1f1f1; padding: 20px; float: left; width: 60%; /* The width is 60%, by default */ } .right { background-color: #04AA6D; padding: 20px; float: left; width: 20%; /* The width is 20%, by default */ } /* Use a media query to add a break point at 800px: */ @media screen and (max-width: 800px) { .left, .main, .right { width: 100%; /* The width is 100%, when the viewport is 800px or smaller */ } } </style> </head> <body> <h2>Media Queries</h2> <p>Resize the browser window.</p> <p>Make sure you reach the breakpoint at 800px when resizing this frame.</p> <div class="left"> <p>Left Menu</p> </div> <div class="main"> <p>Main Content</p> </div> <div class="right"> <p>Right Content</p> </div> </body> </html>