[DevTools] Responsive design UI rework.

Source/devtools/front_end/responsiveDesignView.css

 /*
  * Copyright 2014 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 .responsive-design {
     overflow: hidden;
     position: relative;
 }
@@ skipping 70 matching lines @@
 }
 
 .responsive-design-toolbar fieldset,
 .responsive-design-toolbar p {
     margin: 0;
     padding: 0;
     border: 0;
     display: inline-block;
 }
 
+.responsive-design-screen-section > fieldset,
+.responsive-design-user-agent-section > p {
+    margin-left: 7px;
+}
+
 .responsive-design-toolbar .responsive-design-section {
     display: flex;
     flex: 1 0 auto;
     flex-direction: row;
     height: 24px;
     margin-top: -1px;
     white-space: nowrap;
     align-items: center;
     justify-content: flex-start;
     padding-right: 3px;
@@ skipping 204 matching lines @@
     float: left;
     margin-right: 4px;
     margin-left: 2px;
 }
 
 @media (-webkit-min-device-pixel-ratio: 1.5) {
 .responsive-design-warning::before {
     background-image: url(Images/statusbarButtonGlyphs_2x.png);
 }
 } /* media */