Index: src/wp-admin/css/themes.css
===================================================================
--- src/wp-admin/css/themes.css	(revision 51882)
+++ src/wp-admin/css/themes.css	(working copy)
@@ -465,12 +465,14 @@
 .theme-overlay .theme-wrap {
 	clear: both;
 	position: fixed;
-	top: 9%;
+	top: 30px;
 	left: 190px;
 	right: 30px;
-	bottom: 3%;
+	bottom: 30px;
 	background: #fff;
 	box-shadow: 0 1px 20px 5px rgba(0, 0, 0, 0.1);
+	margin: 32px auto 0; /* Top margin equals the admin toolbar height. */
+	max-width: 1450px;
 	z-index: 10000; /* Over WP Pointers. */
 	box-sizing: border-box;
 	-webkit-overflow-scrolling: touch;
@@ -787,13 +789,6 @@
 	}
 }
 
-@media only screen and (min-width: 1680px) {
-	.theme-overlay .theme-wrap {
-		width: 1450px;
-		margin: 0 auto;
-	}
-}
-
 /* Maximum screenshot width reaches 440px */
 @media only screen and (min-width: 1640px) {
 	.theme-browser .theme {
@@ -838,7 +833,8 @@
 @media only screen and (max-width: 780px) {
 	body.folded .theme-overlay .theme-wrap,
 	.theme-overlay .theme-wrap {
-		top: 0; /* The adminmenu isn't fixed on mobile, so this can use the full viewport height */
+		margin-top: 0; /* The admin toolbar isn't fixed on mobile, so this can use the full viewport height. */
+		top: 0;
 		right: 0;
 		bottom: 0;
 		left: 0;