Firstly I wanna say, please don't use uncannyvally as a how-to-do-this study, its a great looking site, but their code is a disaster! :omg:k: (Their structure is ok-ish, its just very messy, they use WAY too many unnecessary positioning commands and hosting images on discord is not ok!!) :TnT:
Ok so, I interned for a while at a London web advertising agency around 2009, it was still the era when they made sites in this style professionally. The way they did it back then was to design the entire site using Adobe Illustrator, then they would slice it up into fixed standard segments, and export things like buttons as separate images. (Most good graphics editors will have this slice functionality)
The background images would be reassembled around a div (which is a predefined size and was cut out from the original illustrator design) and content would be loaded into the div using php from a database - on neocities we don't use php, so most sites use iFrames to get the same effect.
After that buttons can be positioned on top of the background images using a few simple CSS absolute placements - and because the background was sliced up in known sizes and locked into a div of a fixed size, it should all just snap together!
outer div - 1000px wide
header background (1000px wide)
side background (200px wide) - centre iframe/content div (600px wide) - side background (200px wide)
footer background (1000px wide)
code for buttons (positioned where you like using position absolute)
It can get much more complex depending on how complex your design is and how many windows you want.
As for cinni's site, she uses a much simpler system; she has one background image and then iframes and buttons are positioned on top of it. This design is great for pixel art because the background image can be low-res and resized while still looking good, but its not really usable for a high-res background because it would be super slow to load in a huge background image!
Ooph I hope that was clear and I actually answered your question
- there are a few ways you can make it work, and some will be better or worse depending on what your trying to accomplish! Also I know my knowledge of this kinda site creation is over 10 years old, so maybe there are newer options, but this is the best way I can think to do it!