Set max-width for <video> on CMS pages

services/web/public/stylesheets/app/cms-page.less

@@ -89,4 +89,12 @@
       margin-bottom: @margin-sm;
     }
   }
+
+  /*
+    videos
+  */
+  video {
+    height: auto;
+    max-width: 100%;
+  }
 }