尝试向页面添加雪但它完全消除了我的HTML并且没有显示任何内容

I am trying to add a snowfall background which I got from a css tricks website. The snow looks cool but for some reason the background hides my html content. Please see code below. How can I keep this cool background as EXACTLY THAT, a background so that it does not take over the entire page ? I just need the code to run behind the scene while the html can do its job. I appreciate any help I can get and I know my code is not perfect. Also, I am just learning and again any help I can get is great. I am trying to add a snowfall background which