The _:-webkit-full-screen hack

Last updated 2016-01-12.

The hack

_:-webkit-full-screen, .your-selector-here {
  /* your declarations here */
}

Based upon related hacks by Jeff Clayton (source)

Live testcase

If the square above shows the word "Affected", then your browser supports this hack.

How it works

The underscore is a tag selector that selects <_> elements, which is to say elements whose tagName is "_" (as opposed to e.g. "div"). Of course, HTML doesn't define any <_> element, so this won't match anything, thus preventing this CSS rule from affecting anything besides .your-selector-here.

:-webkit-full-screen is WebKit's prefixed version of the standardized :fullscreen pseudo-class, which matches whenever its element is being displayed in full-screen mode using the WHATWG Fullscreen API. Since Chrome uses Blink, which was forked from WebKit, Chrome also recognizes :-webkit-full-screen. MS Edge has also implemented :-webkit-full-screen for compatibility reasons, despite not having WebKit heritage. As of 2016-01-12, Firefox has refrained from implementing this pseudo-class, though they have been known to implement other WebKit-prefixed CSS entities for compatibility reasons. As of 2016-01-12, for unknown reasons (security or usability perhaps?), Apple has continued to keep support for :-webkit-full-screen disabled on iOS. When browsers see a CSS selector with a pseudo-element they don't recognize, they drop the entire CSS rule associated with it. Thus, only some browsers consider the selector valid and continue parsing it.

Affected browsers

Check out the links for corroborating screenshots.

Test results

Chrome	OS X Safari	iOS Safari	Firefox	MS Edge1	Internet Explorer
48 Unknown	10 Unknown	9.3 Unknown	46 Unknown	13 Unknown
47 Affected	9.0.2 Affected	9.2 Unaffected	45.0a2 Unaffected	12.10240 Affected	11 Unaffected
46 Affected	8.0.8 Affected	8.4 Unaffected	44.0b7 Unaffected	12.10166 Unknown	10 Unaffected
26 Affected	7.1.7 Affected	7.1 Unaffected	43.0.4 Unaffected		9 Unaffected
25 Unknown	6.2.7 Affected	6.1 Unaffected	4.0.1 Unaffected		8 Unaffected
	5.1.7 Affected	5.1 Unaffected			7 Unknown
	4 Unknown	4.3.5 Unknown