created cta-bg variable and changed bg color on light theme (#10693)

public/sass/_variables.dark.scss

@@ -135,6 +135,7 @@ $list-item-bg: $card-background;
 $list-item-hover-bg: lighten($gray-blue, 2%);
 $list-item-link-color: $text-color;
 $list-item-shadow: $card-shadow;
+$empty-list-cta-bg: $gray-blue;
 
 // Scrollbars
 $scrollbarBackground: #404357;

public/sass/_variables.light.scss

@@ -133,6 +133,7 @@ $list-item-bg: linear-gradient(135deg, $gray-5, $gray-6); //$card-background;
 $list-item-hover-bg: darken($gray-5, 5%);
 $list-item-link-color: $text-color;
 $list-item-shadow: $card-shadow;
+$empty-list-cta-bg: $gray-6;
 
 // Tables
 // -------------------------

public/sass/components/_empty_list_cta.scss

 .empty-list-cta {
-  background-color: $search-filter-box-bg;
+  background-color: $empty-list-cta-bg;
   text-align: center;
   padding: $spacer*2;
   border-radius: $border-radius;