Calendar Picker: Make month popup cells non-focusable.

Source/web/resources/calendarPicker.css

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 226 matching lines @@
     padding: 0;
 }
 
 .month-buttons-row {
     display: flex;
 }
 
 .month-button {
     flex: 1;
     height: 32px;
+    line-height: 32px;
     padding: 0 !important;
     margin: 0 !important;
     background-image: none !important;
     background-color: #ffffff;
     border-width: 0 !important;
     box-shadow: none !important;
+    text-align: center;
 }
 
 .month-button.highlighted {
     background-color: #e5ecf8;
 }
 
+.month-button[aria-disabled="true"] {
+    color: GrayText;
+}
+
 .scrubby-scroll-bar {
     width: 14px;
     height: 60px;
     background-color: white;
     border-left: 1px solid #bfbfbf;
     position: absolute;
     top: 0;
 }
 
 .scrubby-scroll-thumb {
@@ skipping 40 matching lines @@
     * This is particularly noticeable on mac. */
     border-color: rgb(77, 144, 254) !important;
     outline: none;
 }
 
 .preparing button:focus,
 .preparing .year-list-view:focus,
 .preparing .calendar-table-view:focus {
     transition: none;
 }