[web_dev_style] Changing :pseudo-element to ::pseudo-element to match

chrome/browser/resources/shared/css/about_version.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. */
 
 body {
   background-color: white;
   color: black;
   font-family: Helvetica,Arial,sans-serif;
   margin: 0;
 }
@@ skipping 12 matching lines @@
 
 .label {
   -webkit-padding-end: 5px;
   font-size: 0.9em;
   font-weight: bold;
   text-align: end;
   vertical-align: top;
   white-space: nowrap;
 }
 
-.label:after {
+.label::after {
   content: ':';
 }
 
 #logo {
   float: right;
   margin-left: 40px;
   text-align: right;
   width: 180px;
 }
 
 #company {
   font-size: 0.7em;
   text-align: right;
 }
 
 #copyright {
   font-size: 0.7em;
   text-align: right;
 }
 
 #useragent {
   font-family: monospace;
 }
 
 .version {
   font-family: monospace;
   max-width: 430px;
   padding-left: 5px;
 }