使用子菜单时消失的内容（菜单和子菜单争夺目标）

What I'm essentially trying to create is a website with multiple image galleries. There is a menu on the left that lets you select from the different galleries. After clicking a menu item, a gallery appears beside it on the right. Each gallery has a large image displayed with smaller thumbnails below it. Clicking a thumbnail changes the large image above it. What I'm essentially trying to create is a webs