Update use of Sass variables for better theming

Use Bootstrap color functions for theme-colors and grays instead
of directly referencing Sass variable to allow more flexible
theming.

Signed-off-by: Yoshie Muranaka <yoshiemuranaka@gmail.com>
Change-Id: Id08b77ff6df3bdf99400dcdfe964853706f1070f
diff --git a/src/views/Overview/OverviewQuickLinks.vue b/src/views/Overview/OverviewQuickLinks.vue
index 5dd71ee..d3a1940 100644
--- a/src/views/Overview/OverviewQuickLinks.vue
+++ b/src/views/Overview/OverviewQuickLinks.vue
@@ -106,7 +106,7 @@
 }
 
 .quicklinks {
-  background: $container-bgd;
+  background: gray('200');
   display: grid;
   grid-gap: 1rem;
   padding: 1rem;