feat(components): add open box symbol

apps/www/src/components/demos/Keycap/Keycap.tsx

@@ -35,7 +35,9 @@ export const KeycapDemo = () => {
           'flex h-9 w-24 items-center justify-center rounded-lg border border-b-4 border-grey-line border-b-grey-text-contrast bg-grey-bg text-sm font-semibold text-grey-text-contrast transition-[border] duration-100 ease-in-out',
           'hover:border-b-[1px] hover:border-grey-line',
         )}
-      />
+      >
+        ␣
+      </button>
 
       <button
         className={clsx(