Fix: Matching dropdown list style improvements (fixes #478) (#507)

* only apply selected styles when a dropdown item has been selected

* apply border to dropdown list to distinguish end of list

* remove bottom border from last item to prevent double up of border

less/plugins/adapt-contrib-matching/dropdown.less

@@ -40,20 +40,29 @@
   }
 }
 
+.dropdown__list {
+  border: 0.19rem solid @item-color-selected;
+}
+
 .dropdown-item {
   padding: @item-padding;
   background-color: @item-color;
   border-bottom: 1px solid @item-color-hover;
   color: @item-color-inverted;
 
-  .no-touch &:not(:focus-visible):not([aria-selected="true"]):hover {
+  &:last-child {
+    border-bottom: none;
+  }
+
+  .no-touch &:not(:focus-visible):hover,
+  .dropdown__btn.is-selected + .dropdown__list &[aria-selected="true"]:hover {
     background-color: @item-color-hover;
     color: @item-color-inverted-hover;
     .transition(background-color @duration ease-in, color @duration ease-in;);
   }
 
   &:focus-visible,
-  &[aria-selected="true"] {
+  .dropdown__btn.is-selected + .dropdown__list &[aria-selected="true"] {
     // This code can be used to style a non-native dropdown as closely
     // as possible to the default browser settings
     // background-color: Highlight;