Editor: A11y: Skip link hidden in editor on medium-small screens.

Adjust the position of the skip link in viewports between 600 and 782 pixels, where they were hidden due to `overflow-y: auto` in the block editor. Ensures that the skip link is visibly available for users on all viewport sizes.

Props sabernhardt, narenin, audrasjb, mukesh27, joedolson, wildworks.
Fixes #63084.

git-svn-id: https://develop.svn.wordpress.org/trunk@59992 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-admin/css/common.css

@@ -3908,6 +3908,10 @@ img {
 		top: -39px;
 	}
 
+	.block-editor-page .screen-reader-shortcut:focus {
+		top: 7px;
+	}
+
 	body {
 		min-width: 240px;
 		overflow-x: hidden;