Accessing TOC on narrow window


I’m writing a book which I expect to export as Styled HTML with TOC and at this point I’m really pleased with the way things are formatted so the output is viewable almost anywhere, even on a smartphone.

I have noticed that when the display width gets small the TOC goes away. Is there a way to get to the TOC when in a window where it doesn’t normally display? Mostly I’m thinking about this on a smartphone where it’s not possible to make the display window larger.