Prevent initial display of modal dialogs when loading.

remoting/webapp/main.css

 /* Copyright (c) 2012 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 html, body, div, span, applet, object, iframe, h1, h2, h3, h4, h5, h6, p,
 blockquote, pre, a, abbr, acronym, address, big, cite, code, del, dfn, em,
 font, img, ins, kbd, q, s, samp, small, strike, strong, sub, sup, tt, var, dl,
 dt, dd, ol, ul, li, fieldset, form, label, legend, table, caption, tbody,
 tfoot, thead, tr, th, td {
@@ skipping 458 matching lines @@
   min-width: 0;
   line-height: 0;
 }
 
 #top-secondary {
   margin-top: 10px
 }
 
 * {
   box-sizing: border-box;
-}
+}
+
+/*
+ * Setting hidden on elements that match some rule overriding 'display' doesn't
+ * do what you would expect unless this is made explicit (and !important).
+ */
+[hidden] {
+  display: none !important;
+}