The template you linked has a couple of issues.

First, it has several syntax errors in the parser functions used in it.

Second, it uses a template "CSS" which is

a) not present on your wiki

b) even if it was can not work on Fandom. There is no way I'm aware of that can use that kind of CSS rules through a template.

I would be interested where you got this from because as said, I'm pretty sure in cannot work.

That said, that template trick using a bloated image with position:fixed and z-index:-1 seen here and there is a pretty hacky way anyway.

The proper way to change the background of a page is using CSS in you site's Common.css file.

The code for this depends on what page(s) you want to use this, what exatly you want the background to look, and what parts of the page be used for.

Example code covering the whole main background:

.page-<pagename> .main-container {
  background-image: url('<path-to-image-here>');
  background-repeat: no-repeat;
  background-size: cover;
}

<pagename> is the name of the page, with spaces and special characters replaced by underlines.

<path-to-image> is the path to your image on the server, usually something like "static.wikia.nocookie.net/path/to/image/.../". You get it when you click on "Original file" on the file description page.

Instead of .main-container, .fandom-community-header__background may be an option which only affects the header of the page.

The background CSS rules may vary for your needs, look up the option for the background property:

https://developer.mozilla.org/en-US/docs/Web/CSS/background

I tried doing that now.

I tried both with <> and without them, it dosent seem to work or should i be more patient?

<> were just to indicate the placeholders.

Remove them both from the url and the page name.

I see, it worked!

I added a little bit more as you said before, to add some more content to my liking.

Thank you! :) i owe you one this one.