MD downloads: add a narrow mode for smaller windows

chrome/browser/resources/md_downloads/item.css

 /* Copyright 2015 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. */
 
 :host {
   @apply(--downloads-shared-style);
   display: flex;
   margin: 32px 0;
 }
 
 :host([hide-date]) {
   margin-top: -16px;
 }
 
-/* Day separators. */
-:host(:not(:first-of-type):not([hide-date])) :-webkit-any(#content-wrapper,
-                                                          #since) {
-  border-top: 1px solid rgba(0, 0, 0, .2);  /* TODO(dbeam): real color. */
-  padding-top: 32px;
-}
-
 #date-container,
 #end-cap {
   flex: 1 0 var(--downloads-side-column-basis);
 }
 
 #date-container > * {
-  -webkit-margin-start: 24px;
   color: #616161;
   font-size: 107.69%;
   font-weight: bold;
 }
 
 :host([hide-date]) #date-container {
   visibility: hidden;
 }
 
 #content {
@@ skipping 100 matching lines @@
 }
 
 #remove {
   --paper-icon-button: {
     height: 16px;
     width: 16px;
   };
   --iron-icon-height: 16px;
   --iron-icon-width: 16px;
 }
+
+@media not all and (max-width: 1024px) {
+  /* Only show date separators in wide mode. */
+  :host(:not(:first-of-type):not([hide-date])) :-webkit-any(#content-wrapper,
+                                                            #since) {
+    border-top: 1px solid rgba(0, 0, 0, .2);  /* TODO(dbeam): real color. */
+    padding-top: 32px;
+  }
+
+  #date-container > * {
+    -webkit-margin-start: 24px;
+  }
+}
+
+@media all and (max-width: 1024px) {
+  /* In narrow windows, put the dates on top instead of on the side. */
+  :host {
+    flex-direction: column;
+  }
+
+  :host([hide-date]) #date-container,
+  #end-cap {
+    display: none;
+  }
+
+  #content {
+    margin: 0 auto;
+  }
+
+  #date-container {
+    flex: none !important;
+    margin: 0 auto 32px;
+    width: var(--downloads-item-width);
+  }
+}