downloads: Make header look more like settings, extensions, history, and

chrome/browser/resources/bookmark_manager/css/bmm.css

 /* Copyright (c) 2012 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. */
 
 html,
 body {
   cursor: default;
   height: 100%;
   margin: 0;
   overflow: hidden;
@@ skipping 241 matching lines @@
 header {
   align-items: center;
   display: flex;
   min-width: 400px;
   padding: 0 12px;
 }
 
 header h2 {
   flex: 1;
   font-weight: normal;
+  line-height: 1;  /* TODO(dbeam): include chrome_shared.css on this page. */
 }
 
 header form {
   flex: none;
 }
 
 .tree-row.drag-on,
 .drag-on {
   background-color: hsla(214, 91%, 85%, .5);
   border: 1px solid hsl(214, 91%, 85%);
@@ skipping 77 matching lines @@
 
   list [editing] input,
   .tree-item [editing] input {
     padding: 3px 0;
   }
 
   .tree-row .expand-icon {
     top: 6px;
   }
 }