DevTools: [SSP] fix "insert style rule" button on mac

Source/devtools/front_end/sidebarPane.css

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2009 Anthony Ricaud <rik@webkit.org>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 182 matching lines @@
     padding: 4px;
     color: #888;
     background-color: #FFFFC2;
 }
 
 .sidebar-pane-button-new-rule {
     background-image: url(Images/paneAddButtons.png);
     background-position: 0 0;
     position: absolute;
     height: 16px;
-    width: 22px;
-    right: 0px;
+    width: 23px;
+    right: 10px;
     bottom: 1px;
     visibility: hidden;
 }
 
 .styles-section.matched-styles:not(.read-only):hover .sidebar-pane-button-new-rule {
     visibility: visible;
 }
 
 .sidebar-pane-button-new-rule:hover {
     background-position: -23px 0;
-}
+}