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http://fullscreen.spec.whatwg.org/#user-agent-level-style-sheet-defaults [[ width:100%; height:100%; ]] Are these redundant since there is already top:0; right:0; bottom:0; left:0;
No, because e.g. "left: 0, right: 0" on an <img> (or any other replaced element) doesn't affect its width in CSS; it just leads to an overconstrained situation in which one of the offsets is ignored.