fullscreen.html

<!DOCTYPE html><html><head><meta charset="utf-8" /><title>:fullscreen Pseudo-Class</title><style type="text/css">:fullscreen body {background-color: #FEE;}h1:fullscreen {font-size: 20vh;}#fs-toggle:not(:fullscreen) {  background-color: #afa;}#fs-toggle:fullscreen {  background-color: #faa;}</style></head><body id="www-meyerweb-com" class="css"><h1>How big am I?  What color?</h1><p>This demo uses the <code>:fullscreen</code> pseudo-class to automatically  change the style of a button used to toggle full-screen mode on and off,  entirely using CSS.</p><button id="fs-toggle">Toggle Fullscreen</button></body></html>