In my case, I try to inspect elements of things I want to change on my page. Since FriendRewind has its own hard coded stylesheet and structure, you might need to override some stuff.
Use a premade layout as a base and change bits of it bc it might be easier for you.
If you want to learn more about HTML and CSS, use the W3Schools site (the og).
Make sure to save everything on either a notepad, Notepad++ or Visual Code Studio, so you don't lose anything (if anything happens to the website, you have backups on your device).
But Notepad is fine for quick saves. :>
You don't need to make anything spectacular on first try. Learn bit by bit. Changing mostly the stylesheet (CSS) is the easiest way for customization. With HTML, unless you want to add more elements, I would stick with putting just text, some imgs and gifs, maybe tiny boxes inside divs with classes (class is basically the name of the div).
It's easier to organise your stuff within a div. If you have a row of pics, put them in a div like div class="sillypics".
Don't know if this helped. This is merely my way of doing things. But, in in your case, i would totally use a premade one as a base, then tweak it on either Notepad++ or VS Code then test it on my Profile.
Srry for the rambling. XD