rename bg-black to bg-primary

+ rename BottomBar to NowPlayingRight

src/utils/useVisibility.ts

@@ -3,7 +3,7 @@ import { useIntersectionObserver } from "@vueuse/core";
 import { Ref, watch } from "vue";
 
 export default function useVisibility(
-  elem: Ref<HTMLElement>,
+  elem: Ref<HTMLElement | null>,
   callback: (state: boolean) => void
 ) {
   const visible = ref(false);