<!DOCTYPE html> <html style="margin:2em;color:red"> <head> <meta charset="UTF-8"> <script> function boom() { document.documentElement.offsetHeight; document.body.style.position = "fixed"; document.documentElement.offsetHeight; document.documentElement.style.MozBoxSizing = "border-box"; document.documentElement.offsetHeight; } </script> </head> <body style="display: contents;" onload="boom();"><li style="color:lime">LI</body></html>