Downloads WebUI: update date text style

Bug: 849857
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: I8b9db90d117d0877c70e1b30b6af1e56cea46535
Reviewed-on: https://chromium-review.googlesource.com/1124925
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573476}

chrome/browser/resources/md_downloads/item.html

@@ -33,8 +33,8 @@
       }
 
       #date {
-        color: var(--paper-grey-700);
-        font-size: 123%;
+        color: var(--google-grey-900);
+        font-size: 0.875rem;
         font-weight: 400;
         letter-spacing: .25px;
         margin: 24px auto 10px;