Increase the style contrast between pressed and un-pressed button states by using enhanced box-shadow to differentiate. Props wildworks, mukesh27, shailu25, maulikmakwana2008, huzaifaalmesbah, sabernhardt, khushi1501, ozgursar, noruzzaman, gaisma22, sirlouen, joedolson. Fixes #64856. Built from https://develop.svn.wordpress.org/trunk@62106 git-svn-id: http://core.svn.wordpress.org/trunk@61388 1a063a9b-81f0-0310-95a4-ce76da25c4cd