DevTools: polish Mac UI (borders, alignment, line heights, images).

Source/devtools/front_end/sourcesPanel.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 52 matching lines @@
     overflow: hidden;
 }
 
 .scripts-debug-toolbar-drawer.expanded {
     margin-top: 0;
 }
 
 .scripts-debug-toolbar-drawer > label {
     display: flex;
     padding-left: 3px;
+    border-top: 1px solid rgb(196,196,196);
 }
 
 #scripts-editor-toolbar {
     position: relative;
     margin-top: -1px;
     height: 24px;
 }
 
 .scripts-run-snippet .glyph {
     -webkit-mask-position: -64px -48px;
@@ skipping 50 matching lines @@
     margin-right: 36px;
 }
 
 .panel.sources .split-view button.scripts-debugger-show-hide-button.right-sidebar-show-hide-button.toggled-hide {
     margin-right: 15px;
 }
 
 .panel.sources .split-view #scripts-debug-sidebar-resizer-widget.ns-resizer-widget {
     -webkit-transform: rotate(90deg);
     right: 17px;
-    bottom: 0;
+    bottom: 1px;
     top: auto;
+    height: 16px;
+    width: 24px;
 }
 
 .panel.sources .split-view.hbox #scripts-debug-sidebar-resizer-widget {
     bottom: 0;
 }
 
 .panel.sources .scripts-debugger-show-hide-button {
     display: block;
 }
 
 .panel.sources button.status-bar-item.scripts-navigator-show-hide-button {
     display: block;
+    left: 4px;
 }
 
 .panel.sources .navigator-tabbed-pane .tabbed-pane-header {
     background-color: rgb(236, 236, 236);
 }
 
 .function-location-link {
     float: right;
     margin-left: 10px;
 }
@@ skipping 43 matching lines @@
 .panel.sources .drag-mask-inner {
     font-size: 30px;
     color: #999;
     display: flex;
     justify-content: center;
     align-items: center;
     margin: 20px;
     border: 4px dashed #ddd;
     pointer-events: none;
 }