Index: src/wp-admin/admin-header.php
===================================================================
--- src/wp-admin/admin-header.php	(revision 36342)
+++ src/wp-admin/admin-header.php	(working copy)
@@ -169,7 +169,10 @@
 	$admin_body_class .= ' network-admin';
 
 $admin_body_class .= ' no-customize-support no-svg';
-
+// Print a CSS class to make PHP errors visible.
+if ( error_get_last() ) {
+	$admin_body_class .= ' php-error';
+}
 ?>
 </head>
 <?php
Index: src/wp-admin/css/admin-menu.css
===================================================================
--- src/wp-admin/css/admin-menu.css	(revision 36342)
+++ src/wp-admin/css/admin-menu.css	(working copy)
@@ -13,6 +13,15 @@
 	z-index: 1; /* positive z-index to avoid elastic scrolling woes in Safari */
 }
 
+.php-error #adminmenuback {
+	position: absolute;
+}
+
+.php-error #adminmenuback,
+.php-error #adminmenuwrap {
+	margin-top: 20px;
+}
+
 #adminmenu {
 	clear: left;
 	margin: 12px 0;