add styling for active menu items

dev/scss/components/_header-menu.scss

@@ -26,12 +26,21 @@
     color: $di-purple;
     font-weight: 700;
 
+    .current-menu-item &,
     &:hover,
     &:active {
       background-color: $di-purple;
       color: $copy-light;
     }
   }
+
+  .current-menu-item {
+    a {
+      background-color: rgba($di-purple, 0.8);
+      color: $copy-light;
+      pointer-events: none;
+    }
+  }
 }
 
 @media screen and (max-width: #{$screen-tablet - 1}) {