Remove any sidebar content from the generated PDF

[Zethson]

Describe the bug

context When I do create a standalone PDF I unfortunately still see the sidebar left. I used some of the in other issues recommended css to get rid of it but had no success.

expectation I expected the three buttons on the right to be gone. They are also not functional.

$ jupyter-book build jupyter-book/ --builder pdfhtml

Reproduce the bug

1. git clone https://github.com/theislab/extended-single-cell-best-practices
2. cd extended-single-cell-best-practices
3. make pdf

List your environment

1. Python 3.9
2. Arch Linux
3. jupyter-book 0.12.3

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