Customize: Fix visibility of "Hide Controls" link in IE.

Amends [39214].
Props timmydcrawford.
See #32296, #38762.
Fixes #40507.

Built from https://develop.svn.wordpress.org/trunk@40510


git-svn-id: http://core.svn.wordpress.org/trunk@40386 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/themes.css

@@ -1520,7 +1520,6 @@ body.full-overlay-active {
 	box-shadow: none !important;
 	-webkit-border-radius: 0 !important;
 	border-radius: 0 !important;
-	z-index: -1; /* Below device buttons */
 }
 
 .wp-core-ui .wp-full-overlay .collapse-sidebar:hover,
@@ -1622,8 +1621,12 @@ body.full-overlay-active {
 	background: #eee;
 }
 
-.wp-full-overlay-footer .devices {
+.wp-full-overlay-footer .devices-wrapper {
 	float: right;
+}
+
+.wp-full-overlay-footer .devices {
+	position: relative;
 	background: #eee;
 	-webkit-box-shadow: -20px 0 10px -5px #eee;
 	box-shadow: -20px 0 10px -5px #eee;