Docs: start redoing landing page

styles/_colors.scss

@@ -112,6 +112,8 @@ $text-muted:      $gray-200;
 $breadcrumb-bg:   $black;
 $breadcrumb-active-color: $gray-400;
 
+$card-bg:   $gray-800;
+
 $dropdown-bg:     $gray-900;
 $dropdown-divider-bg: $black;
 $dropdown-border-color: $gray-900;