<!DOCTYPE html> <html> <head> <style> .site-header { position: relative; z-index: 7; } .dropnav { visibility: hidden; } .dropnav:after { -webkit-backdrop-filter:blur(5px); content:""; height:calc(100vh - 70px); position:fixed; width:100%; } </style> </head> <body> <header class="site-header"> <div class="dropnav"> <span>App</span> </div> </header> <div style="position: relative; top: 100px; left: 100px; width: 200px; height: 200px; background: blue;"></div> </body> </html>