DevTools: make toolbar button click targets square

Source/devtools/front_end/emulation/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 {
     position: relative;
     background-color: rgb(0, 0, 0);
     overflow: hidden;
@@ skipping 299 matching lines @@
 
 .responsive-design-icon-swap:active {
     opacity: 0.8;
 }
 
 /* Buttons section */
 
 .responsive-design-section-buttons {
     padding: 4px 0 0 0;
     background: rgb(17, 17, 17);
-    border-right: 2px solid rgb(0, 0, 0);
 }
 
 .responsive-design-more-button-container {
     flex: auto;
     display: flex;
     justify-content: flex-end;
     align-items: flex-end;
     overflow: hidden;
 }
 
@@ skipping 156 matching lines @@
     pointer-events: none;
 }
 
 .media-inspector-label-right {
     right: 4px;
 }
 
 .media-inspector-label-left {
     left: 4px;
 }