Twenty Seventeen: Make sure skip link works in all versions of Internet Explorer

This also reduces the number of browsers detected and patched with this fix. Most modern browsers have patched this common bug, where an anchor link does not move focus when clicked. Twenty Seventeen will only worry about older versions of Internet Explorer in this regard.

Props afercia, sami.keijonen.

See #38604.

Built from https://develop.svn.wordpress.org/trunk@39135


git-svn-id: http://core.svn.wordpress.org/trunk@39075 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-content/themes/twentyseventeen/assets/js/skip-link-focus-fix.js

@@ -6,11 +6,9 @@
  * Learn more: https://git.io/vWdr2
  */
 ( function() {
-	var isWebkit = navigator.userAgent.toLowerCase().indexOf( 'webkit' ) > -1,
-	    isOpera  = navigator.userAgent.toLowerCase().indexOf( 'opera' )  > -1,
-	    isIe     = navigator.userAgent.toLowerCase().indexOf( 'msie' )   > -1;
+	var isIe = /(trident|msie)/i.test( navigator.userAgent );
 
-	if ( ( isWebkit || isOpera || isIe ) && document.getElementById && window.addEventListener ) {
+	if ( isIe && document.getElementById && window.addEventListener ) {
 		window.addEventListener( 'hashchange', function() {
 			var id = location.hash.substring( 1 ),
 				element;

wp-content/themes/twentyseventeen/style.css

@@ -330,12 +330,6 @@ template {
 	z-index: 100000; /* Above WP toolbar. */
 }
 
-/* Do not show the outline on the skip link target. */
-
-#content[tabindex="-1"]:focus {
-	outline: 0;
-}
-
 /*--------------------------------------------------------------
 # Alignments
 --------------------------------------------------------------*/