Index: wp-admin/css/edit.css
===================================================================
--- wp-admin/css/edit.css	(revision 41650)
+++ wp-admin/css/edit.css	(working copy)
@@ -498,21 +498,41 @@
 	border-style: solid;
 }
 
-.notification-dialog {
+#file-editor-warning {
 	position: fixed;
-	top: 30%;
-	max-height: 70%;
-	left: 50%;
-	width: 450px;
-	margin-left: -225px;
+	z-index: 98;
+	top: 0;
+	right: 0;
+	bottom: 0;
+	left: 0;
+	overflow: auto;
+	text-align: center;
+	-webkit-backface-visibility: hidden;
+	backface-visibility: hidden;
+}
+
+#file-editor-warning::before {
+	content: '';
+	display: inline-block;
+	height: 100%;
+	vertical-align: middle;
+}
+
+#file-editor-warning .notification-dialog {
+	display: inline-block;
+	position: relative;
+	max-width: 450px;
+	width: 100%;
 	background: #fff;
 	box-shadow: 0 3px 6px rgba( 0, 0, 0, 0.3 );
 	line-height: 1.5;
-	z-index: 1000005;
+	z-index: 99;
 	overflow-y: auto;
+	vertical-align: middle;
+	text-align: left;
 }
 
-.notification-dialog-background {
+#file-editor-warning .notification-dialog-background {
 	position: fixed;
 	top: 0;
 	left: 0;
@@ -521,9 +541,15 @@
 	background: #000;
 	opacity: 0.7;
 	filter: alpha(opacity=70);
-	z-index: 1000000;
+	z-index: 97;
 }
 
+@media screen and (max-width: 782px) {
+	.wp-responsive-open #file-editor-warning .notification-dialog {
+		right: -190px;
+	}
+}
+
 #post-lock-dialog .post-locked-message,
 #post-lock-dialog .post-taken-over {
 	margin: 25px;