hello timewatcher!! the answer may surprise you! Behold:
iokodobaba
are you surprised? do you feel terror? I was shocked when I first experienced this word. I could feel my bones trying to escape my flesh. This is a word no human is meant to utter or hear or even conceive of. but it is through its power that corru.observer came to be
its meaning is, "have a plan. work on your big project at least 30 minutes a day. even if it's just planning." that's it!
iokodobaba is what made me able to work on corru.observer despite being continuously burnt out at my old job - 30 minutes doesn't seem like a lot, but it very quickly becomes more than 30 minutes if you get into a flow state, and then that all adds up over the course of a year or two or three!!

the very first page of corru.observer was literally a black circle floating in an inverted 3D CSS box with the basement walls - what would become the entrance. then after a day or two, I added fake lighting and the first moth sprite. then after a few more days, the scanning and readout system in their earliest forms were added... then 24+ months later, we're here!
if you have something you're trying to get done, or you keep falling off working on projects like I know I did before C.O, give it a shot!! I cannot understate the unfathomable effectiveness of iokodobaba.
(but also to answer your question a little more directly - yea it's all html/css/vanilla js. just a lot of work poured into it over time! I use some libraries here and there for little things like audio control and whatnot but no full on frameworks)