Index: wp-admin/css/customize-controls.dev.css
===================================================================
--- wp-admin/css/customize-controls.dev.css	(revision 20980)
+++ wp-admin/css/customize-controls.dev.css	(working copy)
@@ -73,6 +73,7 @@
 
 .customize-section.open .customize-section-content {
 	display: block;
+	background: #fff;
 }
 
 .customize-section-title:after {
@@ -92,11 +93,6 @@
 	display: none;
 }
 
-.customize-section.open .customize-section-title:after {
-	margin-top: -1px;
-	border-width: 0 6px 6px;
-}
-
 .customize-section-title:hover:after {
 	border-color: #aaa transparent;
 }
@@ -105,6 +101,10 @@
 	top: 15px;
 }
 
+#customize-info .customize-section-content {
+	background: transparent;
+}
+
 #customize-info .preview-notice {
 	font-size: 13px;
 	line-height: 24px;