style: dropdown menu with subtle grey hover and list padding

Use bg-hover token for grey mouseover instead of full fg/bg
inversion. Add py-1 padding to dropdown container and px-4 to
items for proper list appearance with margin around items.

src/popup/index.html

@@ -315,11 +315,11 @@
                         </button>
                         <div
                             id="more-menu-dropdown"
-                            class="hidden absolute right-0 top-full mt-1 border border-border bg-bg z-50 whitespace-nowrap"
+                            class="hidden absolute right-0 top-full mt-1 border border-border bg-bg z-50 whitespace-nowrap py-1"
                         >
                             <button
                                 id="btn-export-privkey"
-                                class="block w-full text-left px-3 py-2 text-sm hover:bg-fg hover:text-bg cursor-pointer"
+                                class="block w-full text-left px-4 py-1.5 text-sm hover:bg-hover cursor-pointer"
                             >
                                 Export Private Key
                             </button>