Index: src/wp-admin/css/admin-menu.css
===================================================================
--- src/wp-admin/css/admin-menu.css	(revision 42822)
+++ src/wp-admin/css/admin-menu.css	(working copy)
@@ -330,7 +330,6 @@
 #adminmenu .wp-submenu li {
 	padding: 0;
 	margin: 0;
-	overflow: hidden;
 }
 
 #adminmenu .wp-menu-image img {
@@ -547,16 +546,20 @@
 	padding: 0;
 	position: relative;
 	overflow: visible;
-	line-height: 34px;
 	background: none;
 	color: #aaa;
 	cursor: pointer;
-	outline: 0;
 }
 
-#collapse-button:hover,
+#collapse-button:hover {
+	color: #00b9eb;
+}
+
 #collapse-button:focus {
 	color: #00b9eb;
+	/* Only visible in Windows High Contrast mode */
+	outline: 1px solid transparent;
+	outline-offset: -1px;
 }
 
 #collapse-button .collapse-button-icon,
@@ -566,9 +569,12 @@
 	position: absolute;
 	top: 0;
 	left: 0;
-	line-height: 34px;
 }
 
+#collapse-button .collapse-button-label {
+	top: 8px;
+}
+
 #collapse-button .collapse-button-icon {
 	width: 36px;
 	height: 34px;
Index: src/wp-admin/css/common.css
===================================================================
--- src/wp-admin/css/common.css	(revision 42822)
+++ src/wp-admin/css/common.css	(working copy)
@@ -154,7 +154,9 @@
 	line-height: normal;
 	box-shadow: 0 0 2px 2px rgba(0,0,0,.6);
 	text-decoration: none;
-	outline: none;
+	/* Only visible in Windows High Contrast mode */
+	outline: 2px solid transparent;
+	outline-offset: -2px;
 }
 
 .hidden,
@@ -269,6 +271,8 @@
 	box-shadow:
 		0 0 0 1px #5b9dd9,
 		0 0 2px 1px rgba(30, 140, 190, .8);
+	/* Only visible in Windows High Contrast mode */
+	outline: 1px solid transparent;
 }
 
 .ie8 a:focus {
@@ -275,7 +279,13 @@
 	outline: #5b9dd9 solid 1px;
 }
 
-#adminmenu a:focus,
+#adminmenu a:focus {
+	box-shadow: none;
+	/* Only visible in Windows High Contrast mode */
+	outline: 1px solid transparent;
+	outline-offset: -1px;
+}
+
 .screen-reader-text:focus {
 	box-shadow: none;
 	outline: none;
@@ -609,7 +619,6 @@
 	line-height: normal; /* IE8-IE11 need this for buttons */
 	color: #0073aa; /* some of these controls are button elements and don't inherit from links */
 	cursor: pointer;
-	outline: 0;
 }
 
 .wrap .wp-heading-inline + .page-title-action {
@@ -631,6 +640,8 @@
 .wrap .page-title-action:focus {
 	border-color: #5b9dd9;
 	box-shadow: 0 0 2px rgba( 30, 140, 190, 0.8 );
+	/* Only visible in Windows High Contrast mode */
+	outline: 2px solid transparent;
 }
 
 .wrap h1.long-header {
Index: src/wp-admin/css/forms.css
===================================================================
--- src/wp-admin/css/forms.css	(revision 42822)
+++ src/wp-admin/css/forms.css	(working copy)
@@ -52,6 +52,8 @@
 textarea:focus {
 	border-color: #5b9dd9;
 	box-shadow: 0 0 2px rgba( 30, 140, 190, 0.8 );
+	/* Only visible in Windows High Contrast mode */
+	outline: 2px solid transparent;
 }
 
 /* rtl:ignore */
@@ -236,10 +238,12 @@
 	color: #72777c;
 }
 
-.form-invalid input, .form-invalid input:focus,
-.form-invalid select, .form-invalid select:focus {
+.form-invalid input,
+.form-invalid input:focus,
+.form-invalid select,
+.form-invalid select:focus {
 	border-color: #dc3232 !important;
- box-shadow: 0 0 2px rgba( 204, 0, 0, 0.8 );
+	box-shadow: 0 0 2px rgba( 204, 0, 0, 0.8 );
 }
 
 .form-table .form-required.form-invalid td:after {
Index: src/wp-includes/css/admin-bar.css
===================================================================
--- src/wp-includes/css/admin-bar.css	(revision 42822)
+++ src/wp-includes/css/admin-bar.css	(working copy)
@@ -52,8 +52,7 @@
 #wpadminbar a,
 #wpadminbar a:hover,
 #wpadminbar a img,
-#wpadminbar a img:hover {
-	outline: none;
+#wpadminbar a img:hover {x
 	border: none;
 	text-decoration: none;
 	background: none;
@@ -71,9 +70,13 @@
 #wpadminbar textarea,
 #wpadminbar div {
 	box-shadow: none;
-	outline: none;
 }
 
+#wpadminbar a:focus {
+	/* Inherits transparent outline only visible in Windows High Contrast mode */
+	outline-offset: -1px;
+}
+
 #wpadminbar {
 	direction: ltr;
 	color: #ccc;
Index: src/wp-includes/css/buttons.css
===================================================================
--- src/wp-includes/css/buttons.css	(revision 42822)
+++ src/wp-includes/css/buttons.css	(working copy)
@@ -92,9 +92,12 @@
 	padding: 0 36px;
 }
 
+/* Only visible in Windows High Contrast mode */
 .wp-core-ui .button:active,
 .wp-core-ui .button:focus {
-	outline: none;
+	outline: 2px solid transparent;
+	/* Reset inherited offset from Gutenberg */
+	outline-offset: 0;
 }
 
 .wp-core-ui .button.hidden {
@@ -192,7 +195,6 @@
 	border: 0;
 	border-radius: 0;
 	background: none;
-	outline: none;
 	cursor: pointer;
 	text-align: left;
 	/* Mimics the default link style in common.css */
@@ -213,6 +215,8 @@
 	box-shadow:
 		0 0 0 1px #5b9dd9,
 		0 0 2px 1px rgba(30, 140, 190, .8);
+	/* Only visible in Windows High Contrast mode */
+	outline: 1px solid transparent;
 }
 
 .wp-core-ui .button-link-delete {
@@ -282,7 +286,7 @@
 }
 
 .wp-core-ui .button.button-primary.button-hero {
- box-shadow: 0 2px 0 #006799;
+	box-shadow: 0 2px 0 #006799;
 }
 
 .wp-core-ui .button.button-primary.button-hero.active,
@@ -289,7 +293,7 @@
 .wp-core-ui .button.button-primary.button-hero.active:hover,
 .wp-core-ui .button.button-primary.button-hero.active:focus,
 .wp-core-ui .button.button-primary.button-hero:active {
- box-shadow: inset 0 3px 0 #006799;
+	box-shadow: inset 0 3px 0 #006799;
 }
 
 /* ----------------------------------------------------------------------------