DevTools: [SSP] fix design glitches in "Insert New Rule"

Source/devtools/front_end/elementsPanel.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 173 matching lines @@
 }
 
 .styles-section {
     padding: 2px 2px 4px 4px;
     min-height: 18px;
     white-space: nowrap;
     background-origin: padding;
     background-clip: padding;
     -webkit-user-select: text;
     border-bottom: 1px solid rgb(191, 191, 191);
+    position: relative;
 }
 
 .styles-pane .sidebar-separator {
     border-top: 0px none;
 }
 
 .styles-section.user-rule {
     display: none;
 }
 
@@ skipping 546 matching lines @@
 
 .crumbs .crumb.selected, .crumbs .crumb.selected:hover {
     background-color: rgb(56, 121, 217);
     color: white;
     text-shadow: rgba(255, 255, 255, 0.5) 0 0 0;
 }
 
 .crumbs .crumb:hover {
     background-color: rgb(216, 216, 216);
 }