Index: src/wp-includes/css/wp-auth-check.css
===================================================================
--- src/wp-includes/css/wp-auth-check.css	(revision 31943)
+++ src/wp-includes/css/wp-auth-check.css	(working copy)
@@ -34,6 +34,14 @@
 	box-shadow: 0 3px 6px rgba( 0, 0, 0, 0.3 );
 }
 
+@media screen and ( max-width: 380px ) {
+	#wp-auth-check-wrap #wp-auth-check {
+		left: 0;
+		width: 100%;
+		margin: 0;
+	}
+}
+
 #wp-auth-check-wrap.fallback #wp-auth-check {
 	max-height: 180px;
 	overflow: auto;
@@ -44,12 +52,13 @@
 	-webkit-background-size: 16px 16px;
 	background-size: 16px 16px;
 	height: 100%;
+	overflow: auto;
+	-webkit-overflow-scrolling: touch;
 }
 
 #wp-auth-check-wrap #wp-auth-check-form iframe {
-	height: 100%;
+	height: 98%; /* Scrollbar fix */
 	width: 100%;
-	overflow: auto;
 }
 
 #wp-auth-check-wrap .wp-auth-check-close {
Index: src/wp-includes/js/wp-auth-check.js
===================================================================
--- src/wp-includes/js/wp-auth-check.js	(revision 31943)
+++ src/wp-includes/js/wp-auth-check.js	(working copy)
@@ -49,6 +49,7 @@
 			$('#wp-auth-check-form').append( frame );
 		}
 
+		$( 'body' ).addClass( 'modal-open' );
 		wrap.removeClass('hidden');
 
 		if ( frame ) {
@@ -80,6 +81,7 @@
 		wrap.fadeOut( 200, function() {
 			wrap.addClass('hidden').css('display', '');
 			$('#wp-auth-check-frame').remove();
+			$( 'body' ).removeClass( 'modal-open' );
 		});
 	}
 
@@ -89,14 +91,14 @@
 	}
 
 	$( document ).on( 'heartbeat-tick.wp-auth-check', function( e, data ) {
-		if ( 'wp-auth-check' in data ) {
+		/*if ( 'wp-auth-check' in data ) {
 			schedule();
 			if ( ! data['wp-auth-check'] && wrap.hasClass('hidden') ) {
 				show();
 			} else if ( data['wp-auth-check'] && ! wrap.hasClass('hidden') ) {
 				hide();
 			}
-		}
+		}*/
 	}).on( 'heartbeat-send.wp-auth-check', function( e, data ) {
 		if ( ( new Date() ).getTime() > next ) {
 			data['wp-auth-check'] = true;
@@ -107,6 +109,7 @@
 		wrap.find('.wp-auth-check-close').on( 'click', function() {
 			hide();
 		});
+		show();
 	});
 
 }(jQuery));