DevTools: remove padding before pseudo-element matched styles.

Source/devtools/front_end/elements/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 153 matching lines @@
 }
 
 .styles-section:last-child {
     border-bottom: none;
 }
 
 .styles-pane .sidebar-separator {
     border-top: 0 none;
 }
 
-.styles-sidebar-placeholder {
-    height: 16px;
-}
-
 .styles-section.read-only {
     background-color: #eee;
 }
 
 .styles-section .style-properties li.not-parsed-ok {
     margin-left: 0;
 }
 
 .styles-section .style-properties li.filter-match,
 .styles-section .simple-selector.filter-match {
@@ skipping 541 matching lines @@
 
 .style-properties li.editing-sub-part {
     padding: 3px 6px 8px 18px;
     margin: -1px -6px -8px -6px;
     text-overflow: clip;
 }
 
 .properties-widget-section {
     padding: 2px 0px 2px 5px;
 }