Hi amreus, I'm not sure you've provided a clear enough description of what you want to do. My first thought is that without changing anything from the Vanilla theme, there's a media query that puts the sidebar to full width, at the top of the window, when the screen is narrower than some default. In this mode, on
tiddlywiki.com, the "sidebar" opener/closer is hidden in the hamburger menu.
Does this not work for you or not suit your use case?
Best,
Chris