MD Bookmarks: Fix sidebar min/max width and Add dialog text

chrome/browser/resources/md_bookmarks/app.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/cr/ui/splitter.html">
 <link rel="import" href="chrome://bookmarks/api_listener.html">
 <link rel="import" href="chrome://bookmarks/constants.html">
 <link rel="import" href="chrome://bookmarks/dnd_manager.html">
 <link rel="import" href="chrome://bookmarks/list.html">
 <link rel="import" href="chrome://bookmarks/router.html">
 <link rel="import" href="chrome://bookmarks/shared_vars.html">
 <link rel="import" href="chrome://bookmarks/store.html">
 <link rel="import" href="chrome://bookmarks/toolbar.html">
@@ skipping 18 matching lines @@
 
       #splitter {
         cursor: e-resize;
         flex: 0 0 var(--splitter-width);
       }
 
       :host-context([dir='rtl']) #splitter {
         cursor: w-resize;
       }
 
-      bookmarks-sidebar {
-        max-width: 40%;
-        min-width: var(--min-sidebar-width);
-        width: var(--min-sidebar-width);
-      }
-
       #sidebar {
         -webkit-padding-start: 3px;
         display: block;
+        max-width: 40%;
+        min-width: var(--min-sidebar-width);
         overflow-x: hidden;
         overflow-y: auto;
         padding-top: 8px;
         user-select: none;
+        width: var(--min-sidebar-width);
       }
 
       bookmarks-list {
         flex: 1;
         min-width: 550px;
       }
     </style>
     <bookmarks-toolbar sidebar-width="[[sidebarWidth_]]"></bookmarks-toolbar>
     <div id="main-container">
        <div id="sidebar">
         <bookmarks-folder-node item-id="0" depth="-1"></bookmarks-folder-node>
       </div>
       <div id="splitter"></div>
       <bookmarks-list></bookmarks-list>
     </div>
     <bookmarks-router></bookmarks-router>
   </template>
   <script src="chrome://bookmarks/app.js"></script>
 </dom-module>