<!doctype html> <meta charset="utf-8"> <style> #box { width: 200px; height: 200px; } #top { border-left: 100px solid blue; border-right: 100px solid black; height: 100px; } #bottom { border-left: 100px solid green; border-right: 100px solid red; height: 100px; } </style> <div id="box"> <div id="top"></div> <div id="bottom"></div> </div>