Changing background color or other basic style attributes per page?

I’m trying to figure out the easiest way to change the background color and other basic style attributes per page in WordPress.

Context: I know some css. I don’t know php. I know only basic HTML (like link tags and bold for fonts)

I thought that one way to do this would be make several page templates for my child theme and then – somehow – refer to each template in the style.css to change just the parts I want to change from the default.

So after some searching I did some cut and paste and made a page template php file that is this:

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[code moderated - please follow the forum rules for posting code]

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thinking that I had created a class that I could then code into the style.css. Somehow. The template shows up fine in the page drop-down menu. But I can't figure out how to get it to differ from the default through style.css edits.

1. If I am correct in my approach here and the php file above is ok:

Could someone give me the piece of code I would need in the style.css file to change/override the default background color or image for this template? I don't seem to be able to figure out the syntax. Also, if there is a particular place that this should go or not go in the stylesheet, I would appreciate knowing that too.

2. If I didn't do the php file correctly:

Could someone advise me as to how to change it (and also answer #1 if you're so inclined)

3. OR is there a whole other simpler way to do this that doesn't involve page templates at all?

(for example: I saw a reference somewhere to something along the lines of .page-id=1 followed by specific css attributes but I can't quite figure out the specific code (a correct code example example, say for the background color, would be awesome).

I feel like I should have this figured out already. But clearly I'm missing something rather huge amidst the grand-canyon-size gaps in my actual knowledge.