Index: src/wp-admin/css/colors/_admin.scss
===================================================================
--- src/wp-admin/css/colors/_admin.scss	(revision 38345)
+++ src/wp-admin/css/colors/_admin.scss	(working copy)
@@ -485,6 +485,19 @@
 	border-bottom-color: $highlight-color;
 }
 
+#customize-controls .control-section:hover > .accordion-section-title,
+#customize-controls .control-section .accordion-section-title:hover,
+#customize-controls .control-section.open .accordion-section-title,
+#customize-controls .control-section .accordion-section-title:focus,
+.customize-panel-back:hover,
+.customize-panel-back:focus,
+.customize-section-back:hover,
+.customize-section-back:focus,
+#available-widgets .widget-tpl:hover,
+#available-widgets .widget-tpl.selected {
+	border-left-color: $highlight-color;
+}
+
 /* Responsive Component */
 
 div#wp-responsive-toggle a:before {
Index: src/wp-admin/css/customize-controls.css
===================================================================
--- src/wp-admin/css/customize-controls.css	(revision 38345)
+++ src/wp-admin/css/customize-controls.css	(working copy)
@@ -48,7 +48,6 @@
 
 #customize-controls .customize-info {
 	border: none;
-	border-top: 1px solid #ddd;
 	border-bottom: 1px solid #ddd;
 	margin-bottom: 15px;
 }
@@ -155,6 +154,7 @@
 	color: #555;
 	background-color: #fff;
 	border-bottom: 1px solid #eee;
+	border-left: 4px solid #fff;
 }
 
 #customize-theme-controls .accordion-section-title:after {
@@ -171,10 +171,15 @@
 #customize-controls .control-section .accordion-section-title:hover,
 #customize-controls .control-section.open .accordion-section-title,
 #customize-controls .control-section .accordion-section-title:focus {
-	color: #23282d;
+	color: #191e23;
 	background: #f5f5f5;
+	border-left: 4px solid #0073aa;
 }
 
+#accordion-section-themes + .control-section {
+	border-top: 1px solid #ddd;
+}
+
 .js .control-section:hover .accordion-section-title,
 .js .control-section .accordion-section-title:hover,
 .js .control-section.open .accordion-section-title,
@@ -202,6 +207,11 @@
 	border-bottom-color: #ddd;
 }
 
+#customize-theme-controls .control-panel-content .control-section:nth-child(2),
+#customize-theme-controls .control-panel-nav_menus .control-section:nth-child(3) {
+	border-top: 1px solid #ddd;
+}
+
 #customize-theme-controls > ul {
 	margin: 0;
 }
@@ -329,6 +339,7 @@
 	background: #fff;
 	border: none;
 	border-right: 1px solid #ddd;
+	border-left: 4px solid #fff;
 	-webkit-box-shadow: none;
 	box-shadow: none;
 	cursor: pointer;
@@ -361,6 +372,7 @@
 #customize-controls .panel-meta.customize-info .accordion-section-title:hover {
 	background: #fff;
 	color: #555;
+	border-left: none;
 }
 
 .customize-controls-close:focus,
@@ -381,6 +393,7 @@
 .customize-section-back:focus {
 	color: #23282d;
 	background: #f5f5f5;
+	border-left: 4px solid #0073aa;
 	outline: none;
 	-webkit-box-shadow: none;
 	box-shadow: none;
@@ -399,7 +412,7 @@
 	font: normal 20px/72px dashicons;
 	content: "\f341";
 	position: relative;
-	left: 13px;
+	left: 9px;
 }
 
 .wp-full-overlay-sidebar .wp-full-overlay-header {
@@ -975,17 +988,24 @@
 	animation: customize-reload .75s;
 }
 
-.control-section-themes .accordion-section-title {
+#customize-theme-controls .control-section-themes .accordion-section-title:hover, /* Not a focusable element. */
+#customize-theme-controls .control-section-themes .accordion-section-title {
 	cursor: default;
+	background: #fff;
+	color: #555;
+	border-top: 1px solid #ddd;
+	border-bottom: 1px solid #ddd;
+	border-left: none;
+	margin-top: 0;
 }
 
-#customize-theme-controls .control-section-themes .accordion-section-title:hover,
-#customize-theme-controls .control-section-themes .accordion-section-title:focus {
-	color: #555;
-	background-color: #fff;
+#customize-theme-controls .control-section-themes .customize-themes-panel .accordion-section-title:first-child:hover, /* Not a focusable element. */
+#customize-theme-controls .control-section-themes .customize-themes-panel .accordion-section-title:first-child {
+	border-top: 0;
 }
 
-.control-section-themes .accordion-section-title {
+#customize-theme-controls .control-section-themes > .accordion-section-title:hover, /* Not a focusable element. */
+#customize-theme-controls .control-section-themes > .accordion-section-title {
 	margin: 15px 0;
 }
 
@@ -1442,6 +1462,7 @@
 	padding: 20px 15px 20px 60px;
 	background: #fff;
 	border-bottom: 1px solid #e5e5e5;
+	border-left: 4px solid #fff;
 	cursor: pointer;
 	display: none;
 }
Index: src/wp-admin/css/customize-nav-menus.css
===================================================================
--- src/wp-admin/css/customize-nav-menus.css	(revision 38345)
+++ src/wp-admin/css/customize-nav-menus.css	(working copy)
@@ -1,8 +1,12 @@
-#accordion-section-menu_locations {
+#customize-theme-controls #accordion-section-menu_locations {
 	position: relative;
 	margin-bottom: 15px;
 }
 
+#customize-theme-controls #accordion-section-menu_locations > .accordion-section-title {
+	border-bottom-color: #ddd;
+}
+
 .menu-in-location,
 .menu-in-locations {
 	display: block;
@@ -754,9 +758,14 @@
 
 /* Add/delete Menus */
 
+#customize-theme-controls .control-panel-content .control-section-nav_menu:nth-last-child(2) .accordion-section-title {
+	border-bottom-color: #ddd;
+}
+
 /* @todo update selector */
 #accordion-section-add_menu {
 	margin: 15px 12px;
+	overflow: hidden;
 }
 
 .new-menu-section-content {
Index: src/wp-admin/css/customize-widgets.css
===================================================================
--- src/wp-admin/css/customize-widgets.css	(revision 38345)
+++ src/wp-admin/css/customize-widgets.css	(working copy)
@@ -229,8 +229,9 @@
 
 #available-widgets .widget-tpl:hover,
 #available-widgets .widget-tpl.selected {
-	background: #eee;
+	background: #f5f5f5;
 	border-bottom-color: #ccc;
+	border-left: 4px solid #0073aa;
 }
 
 #customize-controls .widget-title h3 {
Index: src/wp-admin/css/themes.css
===================================================================
--- src/wp-admin/css/themes.css	(revision 38345)
+++ src/wp-admin/css/themes.css	(working copy)
@@ -1485,7 +1485,7 @@
 	position: fixed;
 	bottom: 0;
 	left: 0;
-	width: 300px;
+	width: 299px;
 	height: 45px;
 	border-top: 1px solid #ddd;
 	background: #eee;