DevTools: Refactor network panel overview

Source/devtools/front_end/timeline/timelinePanel.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 498 matching lines @@
     position: absolute;
     height: 19px;
     padding-top: 3px;
 }
 
 .timeline-frame-strip.selected {
     background-color: rgb(56, 121, 217);
     color: white;
 }
 
-#timeline-grid-header {
-    pointer-events: none;
-    height: 20px;
-}
-
 #timeline-graph-records-header {
     pointer-events: none;
     height: 19px;
     padding: 1px 0;
     justify-content: center;
 }
 
 .timeline-utilization-strip {
     z-index: 250;
     overflow: hidden;
@@ skipping 332 matching lines @@
 .timeline-gap {
     flex: none;
 }
 
 .timeline-filmstrip-preview {
     margin-top: 10px;
     max-width: 200px;
     max-height: 200px;
     cursor: pointer;
 }