<!doctype html> <meta charset="utf-8"> <title>CSS Test Reference</title> <style> .container { border: 1px solid green; width: 100px; height: 100px; margin-top: 100px; display: flex; position: relative; } .abspos { position: absolute; top: 0; left: 0; background: orange; height: 20px; width: 20px; } </style> <div class="container"> <div class="abspos"></div> </div>