Fix disappearing menu with lots of folders

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. */
 
 <include src="../search_header.css">
 
 html,
 body {
   cursor: default;
   height: 100%;
@@ skipping 188 matching lines @@
   background-image: -webkit-image-set(
       url(../../../../app/theme/default_100_percent/mac/bookmark_bar_folder.png) 1x,
       url(../../../../app/theme/default_200_percent/mac/bookmark_bar_folder.png) 2x);
 }
 </if>
 
 .main {
   border-top: 1px solid rgb(156, 194, 239);
   display: flex;
   flex: 1;
+  min-height: 0;
 }
 
 .pane,
 .splitter {
   display: flex;
   flex-direction: column;
 }
 
 .pane > :first-child,
 .splitter > :first-child {
@@ skipping 156 matching lines @@
 
   list [editing] input,
   .tree-item [editing] input {
     padding: 3px 0;
   }
 
   .tree-row .expand-icon {
     top: 6px;
   }
 }