Remove blue rectange for focused element.

Remove blue rectange for focused element with .using-mouse-nav class.
Previously CSS selector only selected children of .using-mouse-nav
element that are focused.

Bug: 935252
Change-Id: I338d995ab02076fc9fb671c660d8f397dd1a6898
Reviewed-on: https://chromium-review.googlesource.com/c/1490734Reviewed-by: Kristi Park <kristipark@chromium.org>
Commit-Queue: Gayane Petrosyan <gayane@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635901}

chrome/browser/resources/local_ntp/custom_backgrounds.css

@@ -292,7 +292,8 @@ right, so that every text can stay on its row even on the smallest window */
   display: none;
 }
 
-.using-mouse-nav :focus {
+.using-mouse-nav :focus,
+.using-mouse-nav:focus {
   outline: none;
 }