Devtools UI: Display hint when Network panel is empty

Source/devtools/front_end/network/networkLogView.css

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 599 matching lines @@
     background-color: rgba(56, 121, 217, 0.1);
 }
 
 .network-log-grid .network-node-on-initiator-path {
     background-color: hsla(120, 68%, 54%, 0.2) !important;
 }
 
 .network-log-grid .network-node-on-initiated-path {
     background-color: hsla(0, 68%, 54%, 0.2) !important;
 }
+
+.network-status-pane {
+    color: #777;
+    background-color: white;
+    z-index: 500;
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    text-align: center;
+    padding: 0 20px;
+    overflow: auto;
+}
+
+.network-status-pane > .recording-hint {
+    font-size: 14px;
+    text-align: center;
+    line-height: 28px;
+}