DevTools: make toolbar button click targets square

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 38 matching lines @@
     border-bottom: 1px solid rgb(202, 202, 202);
     background-color: #eee;
 }
 
 .sidebar-pane-title {
     display: flex;
     align-items: center;
     background-color: #eee;
     height: 20px;
     padding: 0 5px;
-    border-top: 1px solid #bbb;
+    border-top: 1px solid #dadada;
     white-space: nowrap;
     overflow: hidden;
     position: relative;
 }
 
 .sidebar-pane-title.expanded,
 .sidebar-pane-title:last-child {
     border-bottom: 1px solid #ddd;
 }
 
@@ skipping 69 matching lines @@
     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;
 }