Restyled the butter bar in Files.app.

chrome/browser/resources/file_manager/css/common.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. */
 
 /* This file contains "borrowed" copy of standard styles. To simplify merging,
  * when altering, please preserve original property value by adding comments. */
 input.common[type='checkbox'],
 input.common[type='radio'] {
   -webkit-appearance: none;
   -webkit-border-radius: 1px;
@@ skipping 362 matching lines @@
 button[disabled]:hover,
 input[type='button'][disabled]:hover,
 input[type='submit'][disabled]:hover {
   -webkit-box-shadow: none;
   background: -webkit-linear-gradient(#fafafa, #f4f4f4 40%, #e5e5e5);
   border-color: #aaa;
   color: #888;
 }
 
 /* Blue progress bar. */
-.progress-bar {
+body:not([new-ui]) .progress-bar {
   background-color: #e6e6e6;
   border: 1px solid #ddd;
   border-radius: 2px;
   box-sizing: border-box;
   margin: 2px 0;
 }
 
-.progress-track {
+body:not([new-ui]) .progress-track {
   background-image: -webkit-linear-gradient(
       rgb(110, 188, 249) 1px, rgb(86, 167, 247) 2px,
       rgb(76, 148, 245) 11px, rgb(41, 112, 211) 12px);
   border: 1px solid rgb(65, 137, 237);
   border-radius: 2px;
   height: 10px;
   margin: -1px;
 }
 
+body[new-ui] .progress-bar {
+  background-color: #e6e6e6;
+  border-radius: 3px;
+  height: 6px;
+}
+
+body[new-ui] .progress-track {
+  background-color: #888;
+  border-radius: 3px;
+  height: 6px;
+}
+
 .progress-track.smoothed {
   -webkit-transition: width 1s linear;
 }
 
 /* Icons for the action choice dialog and choosing the default app. */
 div.import-photos-to-drive-icon {
   background-image: -webkit-image-set(
     url('../images/media/drive.png') 1x,
     url('../images/media/2x/drive.png') 2x);
 }
 
 div.view-files-icon {
   background-image: -webkit-image-set(
     url('../images/icon32.png') 1x,
     url('../images/icon64.png') 2x);
 }
 
 div.watch-single-video-icon {
   background-image: -webkit-image-set(
     url('../images/media/watch.png') 1x,
     url('../images/media/2x/watch.png') 2x);
 }