[NTP] Change back the gear icon css setting on dark/image

After experiment, the hover state on dark/image of the gear icon should
be lighter instead of darker to make it visible. Also change the active
state setting for gear icon on dark/image

Bug: 867768
Change-Id: I1b993297788ed6145ac7a32acfd85b766bd67999
Reviewed-on: https://chromium-review.googlesource.com/1197410Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Weilun Shi <sweilun@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587841}

chrome/browser/resources/local_ntp/custom_backgrounds.css

@@ -39,6 +39,14 @@ html[dir=rtl] #edit-bg {
   background-color: rgba(32, 33, 36, .16);
 }
 
+.non-white-bg #edit-bg:hover {
+  background-color: rgba(255, 255, 255, .1);
+}
+
+.non-white-bg #edit-bg:active {
+  background-color: rgba(255, 255, 255, .16);
+}
+
 .using-mouse-nav .bg-option:focus {
   outline: none;
 }