Make sidebar width customizable

[dz4k]

Discussed in #37

^{Originally posted by t1 November 12, 2023}
Missing is just cool. Thanks!

I need a little bit more space in my sidebar. I didn't find a hint in the docs and my experiments with using a grid actually flipped it to horizontal 🤔. Do I really have to resort to a width style attribute?

Whatever the solution, it might be worth adding a hint to the docs.