Index: src/wp-admin/css/customize-controls.css
===================================================================
--- src/wp-admin/css/customize-controls.css	(revision 29896)
+++ src/wp-admin/css/customize-controls.css	(working copy)
@@ -208,7 +208,8 @@
 	transition: color .1s ease-in-out, background .1s ease-in-out;
 }
 
-.control-panel-back {
+.control-panel-back,
+.expand-controls {
 	display: block;
 	position: fixed;
 	top: 0;
@@ -224,14 +225,26 @@
 	transition: left .18s ease-in-out, color .1s ease-in-out, background .1s ease-in-out;
 }
 
-.collapsed .control-panel-back {
+.expand-controls {
+	padding-right: 0;
+	transition: none;
+}
+
+.collapsed .control-panel-back,
+.collapsed .customize-controls-close {
 	display: none;
 }
 
+.collapsed .expand-controls {
+	left: 0;
+}
+
 .customize-controls-close:focus,
 .customize-controls-close:hover,
 .control-panel-back:focus,
-.control-panel-back:hover {
+.control-panel-back:hover,
+.expand-controls:focus,
+.expand-controls:hover {
 	background: #ddd;
 	border-color: #ccc;
 	color: #000;
@@ -256,6 +269,18 @@
 	left: 13px;
 }
 
+.expand-controls:before {
+	font: normal 20px/1 dashicons;
+	content: "\f345";
+	position: relative;
+	top: 7px;
+	left: 13px;
+}
+
+.rtl .expand-controls:before {
+	content: "\f341";
+}
+
 .rtl .control-panel-back:before {
 	content: "\f344";
 }
@@ -431,9 +456,11 @@
 	box-shadow: none !important;
 	-webkit-border-radius: 0 !important;
 	border-radius: 0 !important;
+	position: fixed;
+	left: 0;
+	bottom: 0;
 }
 
-
 .collapse-sidebar:active,
 .collapse-sidebar:active .collapse-sidebar-label,
 .collapse-sidebar:active .collapse-sidebar-arrow:before {
@@ -440,10 +467,57 @@
 	text-shadow: none;
 }
 
-.collapsed .collapse-sidebar-arrow:before {
-	color: #888;
+/* Collapsed Mode */
+@media screen and (min-width:600px) {
+	.collapsed #customize-preview {
+		left: 46px;
+	}
+
+	.wp-full-overlay.collapsed #customize-controls {
+		margin-left: 0;
+		width: 46px;
+		white-space: nowrap;
+	}
+
+	.collapsed .wp-full-overlay-main {
+		right: 0;
+		width: auto;
+	}
+
+	.collapsed #customize-info,
+	.collapsed #customize-controls .accordion-section-title:after {
+		display: none;
+	}
+
+	.collapsed .control-section .accordion-section-title,
+	.collapsed .control-panel .accordion-section-title { 
+		white-space: nowrap;
+		overflow: hidden;
+		text-overflow: ellipsis;
+	}
+
+	.collapsed #customize-controls .wp-full-overlay-sidebar-content {
+		overflow-y: hidden;
+	}
+
+	/* No animation fading in, as it causes layout issues */
+	.expanded.wp-full-overlay,
+	.expanded #customize-preview,
+	.expanded #customize-controls {
+		transition: none;
+	}
+
+	.in-sub-panel.wp-full-overlay,
+	.collapsed.wp-full-overlay,
+	.in-sub-panel #customize-preview,
+	.collapsed #customize-preview,
+	.collapsed #customize-controls {
+		transition: all .2s linear;
+	}
+
 }
 
+
 /* Style for custom settings */
 
 /*
Index: src/wp-admin/css/themes.css
===================================================================
--- src/wp-admin/css/themes.css	(revision 29896)
+++ src/wp-admin/css/themes.css	(working copy)
@@ -1464,7 +1464,7 @@
 
 /* Collapse Button */
 .wp-full-overlay a.collapse-sidebar {
-	position: absolute;
+	position: fixed;
 	bottom: 12px;
 	left: 0;
 	z-index: 50;
@@ -1483,11 +1483,6 @@
 	color: #0074a2;
 }
 
-.wp-full-overlay.collapsed .collapse-sidebar {
-	position: absolute;
-	left: 100%;
-}
-
 .wp-full-overlay .collapse-sidebar-arrow {
 	position: static;
 	margin-top: 0;
Index: src/wp-admin/customize.php
===================================================================
--- src/wp-admin/customize.php	(revision 29896)
+++ src/wp-admin/customize.php	(working copy)
@@ -122,6 +122,7 @@
 				<span class="screen-reader-text"><?php _e( 'Cancel' ); ?></span>
 			</a>
 			<span class="control-panel-back" tabindex="-1"><span class="screen-reader-text"><?php _e( 'Back' ); ?></span></span>
+			<span class="expand-controls" tabindex="-1"><span class="screen-reader-text"><?php _e( 'Expand controls' ); ?></span></span>
 		</div>
 
 		<?php
@@ -173,7 +174,7 @@
 		<div id="customize-footer-actions" class="wp-full-overlay-footer">
 			<a href="#" class="collapse-sidebar button-secondary" title="<?php esc_attr_e('Collapse Sidebar'); ?>">
 				<span class="collapse-sidebar-arrow"></span>
-				<span class="collapse-sidebar-label"><?php _e('Collapse'); ?></span>
+				<span class="collapse-sidebar-label"><?php _e( 'Collapse controls' ); ?></span>
 			</a>
 		</div>
 	</form>
Index: src/wp-admin/js/customize-controls.js
===================================================================
--- src/wp-admin/js/customize-controls.js	(revision 29896)
+++ src/wp-admin/js/customize-controls.js	(working copy)
@@ -1185,14 +1185,33 @@
 				this.click();
 		});
 
+		$('.expand-controls').on( 'click keydown', function( event ) {
+			overlay.toggleClass( 'collapsed' ).toggleClass( 'expanded' );
+		});
+
 		$('.collapse-sidebar').on( 'click keydown', function( event ) {
-			if ( event.type === 'keydown' &&  13 !== event.which ) // enter
+			if ( event.type === 'keydown' &&  13 !== event.which ) { // enter
 				return;
+			}
 
 			overlay.toggleClass( 'collapsed' ).toggleClass( 'expanded' );
+			$('.control-section.open .accordion-section-title').trigger( 'click' );
+			if ( overlay.hasClass('in-sub-panel') ) {
+				$('.control-panel-back').trigger( 'click' );
+			}
 			event.preventDefault();
 		});
 
+		$('.accordion-section-title').on( 'click keydown', function( event ) {
+			if ( event.type === 'keydown' &&  13 !== event.which ) { // enter
+				return;
+			} else if ( overlay.hasClass( 'collapsed' ) ) {
+				if ( ! $( this ).closest( '.control-section' ).hasClass( 'open' ) ) {
+					$( '.expand-controls' ).trigger( 'click' );				
+				}
+			}
+		});
+
 		// Bind site title display to the corresponding field.
 		if ( title.length ) {
 			$( '#customize-control-blogname input' ).on( 'input', function() {