Enable the keyboard to show the popup keyboard for inputting accented characters.

chrome/browser/resources/keyboard/main.css

 /*
 Copyright (c) 2011 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.
 */
 
 body {
   background: -webkit-linear-gradient(#131925, #04070B);
   color: white;
   margin: 0;
@@ skipping 52 matching lines @@
   white-space: nowrap;
 }
 
 .panel {
   border: 0;
   clear: both;
   margin-left: 5px;
   text-align: left;
 }
 
+.popup {
+  background: rgba(30, 30, 30, 0.7);
+  border: 1px solid rgba(50, 50, 50, 0.8);
+  padding-right: 5px;
+  position: absolute;
+  -webkit-border-radius: 4px;
+  -webkit-box-shadow: 5px 5px 3px rgba(50, 50, 200, 0.3);
+}
+
 .button {
   background: -webkit-linear-gradient(#5a616f, #505662);
 }
 .button:active {
   background: -webkit-linear-gradient(#505662, #5a616f);
 }
 
 .auxiliary:active {
   background: -webkit-linear-gradient(#5a616f, #505662);
 }
@@ skipping 11 matching lines @@
 
 .key > div {
   bottom: 0;
   left: 0;
   margin: auto;
   position: absolute;
   right: 0;
   top: 0;
 }
 
+.key.popupkey {
+  background: rgba(0, 0, 0, 0);
+  border: 1px solid rgba(0, 0, 0, 0);
+}
+
+.key.popupkey.highlighted {
+  background: rgba(20, 20, 200, 0.3);
+}
+
 .r0 {
   background: -webkit-linear-gradient(#5a616f, #505662);
 }
 .r0:active {
   background: -webkit-linear-gradient(#505662, #5a616f);
 }
 
 .r1 {
   background: -webkit-linear-gradient(#505662, #41464f);
 }
@@ skipping 94 matching lines @@
 }
 
 .handwriting-clear,
 .handwriting-return {
   -webkit-box-flex: 5;
 }
 
 .nodisplay {
   display: none;
 }