WebUI: fix icon CSS for cr-icons

Bug: 967610
Change-Id: I8a6c2f080a4f9d984ca186fece34b8c715f24afa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632812Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663996}

ui/webui/resources/cr_elements/cr_icons_css.html

@@ -98,7 +98,7 @@
                                          .cr-icon).icon-more-vert {
         background-image: url(../images/dark/icon_more_vert.svg);
       }
-      :-webkit-any(paper-n-button, .cr-icon).icon-more-vert-light-mode {
+      :-webkit-any(cr-icon-button, .cr-icon).icon-more-vert-light-mode {
         background-image: url(../images/icon_more_vert.svg);
       }