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!
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