Settings: Put paper-icon-button-light's inner button in correct place.

Bug: 854560
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: I48820701f46e82e27a488f1b2b5a7feaaa20e436
Reviewed-on: https://chromium-review.googlesource.com/1108752Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569421}

ui/webui/resources/cr_elements/cr_icons_css.html

@@ -13,6 +13,10 @@
         opacity: 0.6;
       }
 
+      paper-icon-button-light button {
+        display: block;
+      }
+
       paper-icon-button-light,
       .cr-icon {
         @apply --cr-paper-icon-button-margin;