Do I have to use [ol,] or [ul,] or can I just use [li] instead, and does it matter?

HTML & CSS
8

What’s the reason for this:

How come margin 0; doesn’t move it all the way to the top left when using [ul]?

It doesn’t here: https://jsfiddle.net/pk5femLr/13/ With [ul]

But it does on here: but that’s only without the ul?
It does here: https://jsfiddle.net/pk5femLr/8/ without [ul]