[MD Bookmarks] Fix outline clipping on sidebar

This CL fixes a clipping issue on the focus ring of a folder node in the
MD Bookmark manager sidebar.

Bug: 845736
Change-Id: I12fd4b6b01c11485d7d334c2567d76f750f568a7
Reviewed-on: https://chromium-review.googlesource.com/1107521
Commit-Queue: calamity <calamity@chromium.org>
Reviewed-by: Scott Chen <scottchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569197}

chrome/browser/resources/md_bookmarks/app.html

@@ -52,12 +52,11 @@
       }
 
       #sidebar {
-        -webkit-padding-start: 3px;
         display: block;
         max-width: 40%;
         min-width: var(--min-sidebar-width);
         overflow-y: auto;
-        padding-top: 8px;
+        padding: 8px 3px 0 3px;
         user-select: none;
         width: var(--min-sidebar-width);
       }