WebUI: Increase contrast for focused cr-action-menu option.

Fixed: 1107917
Change-Id: Ia07198fc4301bf8903586ea16a9f25f5257a1a90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2392978
Commit-Queue: dpapad <dpapad@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Auto-Submit: dpapad <dpapad@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804417}

ui/webui/resources/cr_elements/shared_vars_css.html

@@ -89,7 +89,7 @@
     --cr-hairline-rgb: 0, 0, 0;
     --cr-link-color: var(--google-blue-700);
     --cr-menu-background-color: white;
-    --cr-menu-background-focus-color: var(--google-grey-200);
+    --cr-menu-background-focus-color: var(--google-grey-400);
     --cr-menu-shadow: 0 2px 6px var(--paper-grey-500);
     --cr-separator-color: rgba(0, 0, 0, .06);
     --cr-title-text-color: rgb(90, 90, 90);
@@ -110,7 +110,7 @@
       --cr-hairline-rgb: 255, 255, 255;
       --cr-link-color: var(--google-blue-refresh-300);
       --cr-menu-background-color: var(--google-grey-900);
-      --cr-menu-background-focus-color: rgba(var(--google-grey-800-rgb), .6);
+      --cr-menu-background-focus-color: var(--google-grey-refresh-700);
       --cr-menu-background-sheen: rgba(255, 255, 255, .06);  /* Only dark mode. */
       --cr-menu-shadow: rgba(0, 0, 0, .3) 0 1px 2px 0,
                         rgba(0, 0, 0, .15) 0 3px 6px 2px;