Creator here - this was much more technically difficult than it seems, because rendering pixel perfect backgrounds with scaling width is non-obvious. Hit 'Esc' and you can set some options, including changing the background pattern.

If you want to see a big file, I have a direct link to load the Blocktronics WTF4 ANSI which is over 4000 lines: https://sure.is/ansi/?wtf4=1