guys, how do i add new stuff into an already existing layout

ok so i found this cool monochrome layout by a cool user called whomists (link), but while using the preview site, i found out that a few thinks went broken with time, and i also planned adding music, an animated pfp (scrapped that), contact icons, a loading screen, etc, but i dunno how to do that without messing up the code

in what order do i need to put the new codes for that?