<!DOCTYPE html><style>html{background:red;/* an "L" shape */clip-path:polygon(50px50px,100px50px,100px100px,150px100px,150px150px,50px150px);will-change:transform;}div{width:500px;height:500px;background:green;}</style><linkrel="help"href="http://www.w3.org/TR/css-masking-1/#the-clip-path"><linkrel="help"href="https://drafts.fxtf.org/compositing/#rootgroup"><linkrel="help"href="https://drafts.fxtf.org/compositing/#pagebackdrop"><linkrel="match"href="reference/clip-path-document-element-ref.html"><metaname="assert"content="Clip-path on the document element applies to the root background. The test passes if there is a green 'L' shape without red."><div></div>