sorry i missed your question, but to work on your site offline, you can download your files to your computer and just edit them there, using a text editor to open your html files. you can still use your browser to look at the pages, but you dont actually need internet!
I haven't been active too recently, but I'm still here ^^ busy with offline things and working on my rainbow pages locally on my computer (I should do this anyways rather than directly on neocities, but I've really been doing it bc I have limited data)
i just looked through your whole webpage & wow is it cool! i especially like the different themes, and the accessibility (playing/pausing gifs is such a cool and necessary feature). i also loooved the kitten images, those smol bbs looked like rats! /positive. plus the gif page is something i could stare at forever.......... :)
Notepad is the best for it.
Notepad++ is great but I use Visual Studio Code right now, its search and replace feature works across multiple files if you need it
geany's also pretty good as a text editor for free