diff --git a/app/views/shell/_top.html.erb b/app/views/shell/_top.html.erb
index 23733a678..6642fa8b7 100644
--- a/app/views/shell/_top.html.erb
+++ b/app/views/shell/_top.html.erb
@@ -64,6 +64,7 @@
               --accent-brand: <%= SiteConfig.primary_brand_color_hex %>;
               --accent-brand-darker: <%= HexComparer.new([SiteConfig.primary_brand_color_hex]).brightness(0.85) %>;
               --accent-brand-lighter: <%= HexComparer.new([SiteConfig.primary_brand_color_hex]).brightness(1.1) %>;
+              --accent-brand-a10: <%= HexComparer.new([SiteConfig.primary_brand_color_hex]).opacity(0.1) %>;
             }
           </style>
         </div>