[ntp] Increase margin for text label

Screenshot: screenshot/APu6DvaSHpohUK2

Fixed: 1077441
Change-Id: Ibceaba90a40a28be5b8997edc7e44a801156dc76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2578124
Commit-Queue: Andre Vincent <andrevincent@google.com>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834793}

chrome/browser/resources/new_tab_page/customize_backgrounds.html

@@ -34,7 +34,7 @@
   .label {
     color: var(--cr-primary-text-color);
     margin-bottom: 4px;
-    margin-top: 3px;
+    margin-top: 12px;
     min-height: 30px;
   }