Dropdown Menu: Add default elevation (#684)

* feat(dropdown-menu): add elevation token

Adds a default elevation to the dropdown-menu set
to elevation level 3.

* feat(dropdown-menu): remove border

With the new elevation styles, the border is no longer needed.

Author: brentswisher

.changeset/quiet-garlics-compete.md

@@ -0,0 +1,5 @@
+---
+'@ithaka/pharos': minor
+---
+
+Add default elevation and remove border from dropdown-menu

packages/pharos/src/components/dropdown-menu/pharos-dropdown-menu.scss

@@ -19,8 +19,8 @@
   list-style-type: none;
   padding-left: 0;
   padding-inline-start: 0;
-  border: 1px solid var(--pharos-dropdown-menu-color-border-base);
   border-radius: 2px;
+  box-shadow: var(--pharos-elevation-level-3);
   visibility: hidden;
   pointer-events: none;
   opacity: 0;
@@ -29,10 +29,6 @@
     opacity var(--pharos-transition-duration-short) linear;
 }
 
-:host([is-on-background]) .dropdown-menu__list {
-  border: none;
-}
-
 :host([open]) .dropdown-menu__list {
   visibility: visible;
   opacity: 1;