Index: src/wp-admin/css/common.css
===================================================================
--- src/wp-admin/css/common.css	(revision 33526)
+++ src/wp-admin/css/common.css	(working copy)
@@ -164,6 +164,15 @@
 	display: none;
 }
 
+/* hide UI sections and allow inner sections to be visible */
+.hidden-visibility {
+	visibility: hidden;
+}
+
+.visible-visibility {
+	visibility: visible;
+}
+
 /* @todo: Take a second look. Large chunks of shared color, from the colors.css merge */
 .widget-top,
 .menu-item-handle,
Index: src/wp-admin/js/customize-controls.js
===================================================================
--- src/wp-admin/js/customize-controls.js	(revision 33526)
+++ src/wp-admin/js/customize-controls.js	(working copy)
@@ -3041,7 +3041,7 @@
 			return;
 		}
 
-		var parent, topFocus,
+		var parent,
 			body = $( document.body ),
 			overlay = body.children( '.wp-full-overlay' ),
 			title = $( '#customize-info .panel-title.site-title' ),
@@ -3555,13 +3555,6 @@
 
 		api.trigger( 'ready' );
 
-		// Make sure left column gets focus
-		topFocus = closeBtn;
-		topFocus.focus();
-		setTimeout(function () {
-			topFocus.focus();
-		}, 200);
-
 	});
 
 })( wp, jQuery );
Index: src/wp-includes/js/customize-loader.js
===================================================================
--- src/wp-includes/js/customize-loader.js	(revision 33526)
+++ src/wp-includes/js/customize-loader.js	(working copy)
@@ -208,6 +208,8 @@
 				document.title = this.originalDocumentTitle;
 			}
 
+			Loader.body.removeClass( 'hidden-visibility' );
+
 			// Return focus to link that was originally clicked.
 			if ( this.link ) {
 				this.link.focus();
@@ -231,7 +233,9 @@
 		 * Callback for the `load` event on the Customizer iframe.
 		 */
 		loaded: function() {
-			Loader.body.removeClass('customize-loading');
+			// Make the overlay the only visible and focusable content.
+			Loader.body.removeClass( 'customize-loading' ).addClass( 'hidden-visibility' );
+			Loader.element.addClass( 'visible-visibility' );
 		},
 
 		/**