Make all checkboxes uniformly darker.

chrome/browser/resources/file_manager/css/file_manager.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 {
   height: 100%;
 }
 
 html.col-resize * {
   cursor: col-resize !important;
@@ skipping 1024 matching lines @@
   -webkit-box-align: center;
 }
 
 .file-checkbox {
   -webkit-margin-end: 0;
   -webkit-margin-start: 0;
   position: relative;
   z-index: 2;
 }
 
-.file-checkbox,
-.pin {
-  opacity: 0.3;
-}
-
 #select-all-checkbox {
   -webkit-margin-end: 11px;
   -webkit-margin-start: 1px;
   margin-bottom: 0;
   margin-top: 0;
   /* 1px below text */
   position: relative;
   top: 1px;
 }
 
 #list-container li.table-row:hover .file-checkbox,
 #list-container li.table-row:hover .pin,
 #list-container li.thumbnail-item:hover .file-checkbox {
-  opacity: 0.5;
+  opacity: 0.6;
 }
 
-.file-checkbox:hover,
-.pin:hover,
 #list-container li.table-row[selected] .file-checkbox,
 #list-container li.table-row[selected] .pin,
-#list-container li.table-row .pin:checked,
 #list-container li.thumbnail-item[selected] .file-checkbox {
-  opacity: 0.8 !important;
+  opacity: 1.0 !important;
 }
 
 #list-container li.table-row,
 #default-actions-list li {
   border: none;
   border-top: 1px solid transparent;
   height: 39px;
   padding-bottom: 1px;
   padding-top: 1px;
 }
@@ skipping 460 matching lines @@
   background-color: #ececec;
 }
 
 button:focus {
   outline-color: rgb(77, 144, 254);
 }
 
 #new-folder {
   margin-right: 30px;
 }