Update md-grid-layout.html

Author: gdevacc12

app-grid/demo/md-grid-layout.html

@@ -52,6 +52,7 @@
           --app-grid-gutter: 10px;
           --app-grid-expandible-item-columns: 4;
           --paper-icon-button-ink-color: white;
+          --app-grid-item-height: 200px;
         }
 
         app-header {
@@ -94,7 +95,7 @@
           padding: 16px;
         }
 
-        @media(max-width: 799px) {
+        @media screen and (max-width: 799px) {
 
           .centered-container {
             margin: 10px 5px;