ChromeOS OOBE: Fix keyboard focusing of OOBE buttons.

chrome/browser/resources/chromeos/login/oobe_welcome_secondary_button.css

 /* Copyright 2016 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. */
 :host {
+  color: #5a5a5a;
+  height: 32px; /* = 28 + 2 * 2px keyboad-focus border */
+  max-width: 300px;
+  min-width: 120px;
+}
+
+#button {
+  --paper-button-flat-keyboard-focus: {
+    border-color: rgba(66, 133, 244, 0.4); /* #4284f4 */
+    border-radius: 2px;
+    border-style: solid;
+    border-width: 2px;
+  };
+  height: 100%;
+  margin: 0;
+  padding: 0;
+  width: 100%;
+}
+
+#button:not([focused]) {
+  border-color: transparent;
+  border-radius: 2px;
+  border-style: solid;
+  border-width: 2px;
+}
+
+#container {
   border-color: rgba(0, 0, 0, 0.2);
   border-radius: 2px;
   border-style: solid;
   border-width: 1px;
-  color: #5a5a5a;
-  height: 28px;
-  max-width: 300px;
-  min-width: 120px;
 }
 
-#container {
-  height: 100%;
-  margin: 0;
+#subcontainer {
   padding: 0 16px 0 16px;
 }
 
 ::content * {
   font: var(--oobe-roboto-medium), sans-serif;
   font-size: 12px;
   text-transform: none;
 }
 
 iron-icon {
   --iron-icon-height: 16px;
   --iron-icon-width: 16px;
   color: #5a5a5a;
   margin: 0 8px 0 0;
 }