use path.join instead

src/app/ygopro/ygopro.component.ts

@@ -123,7 +123,7 @@ export class DeckAndCategory {
   }
 
   get symbol() {
-    return `${this.category}/${this.deck}`;
+    return path.join(this.category, this.deck);
   }
 
   set symbol(str: string) {