Trying to make a static (Or parallax) background image on the Rally template?

I've tried several different CSS codes for placing a static (or parallax) image as my background.  I was able to upload the file in the Custom CSS > Manage Uploads section, and got the long URL for that specific image.  The code I'm using is:

body {
 background-image: url("https://static1.squarespace.com/static/5d71ceb59079ce0001c671f5/t/5eb6c7fbb2acbe6aa4bc1ce0/1589037051337/96808.jpg");
}

I've tried several combinations of this including adding comment fields and whatnot, but no matter what I do, my background stays the same and doesn't change to an image.  I've tested on both Firefox and Safari.  

I love the rally template but I can never seem to find any support for it in the main support documents, they always list other templates and act like rally doesn't exist.  rally doesn't have a background image site style option or I would use that. 

I then tried this code:
 

body, html {
  height: 100%;
}

.parallax { 
  /* The image used */
  background-image: url("https://static1.squarespace.com/static/5d71ceb59079ce0001c671f5/t/5eb6c7fbb2acbe6aa4bc1ce0/1589037051337/96808.jpg");

  /* Full height */
  height: 100%; 

  /* Create the parallax scrolling effect */
  background-attachment: fixed;
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}

And it still does not appear on any browser *shrug*

Can you share link to your site?