Check out this thread or the GitHub repository linked to within the thread: "How to achieve" CSS code snippets
There is a css file called Embeds, I think, that has what you are looking for if you read through the comments and cut and paste and adjust the values to achieve what you are looking for.
Hope this helps. I know it helped me for that same goal, although I wasn’t exporting to PDF.
In addition to the above, you can modify your css such that it looks differently only for the PDF: How to style the PDF with @media print?
Does this include changing the background-color of the body? I’ve been searching for hours to get this working but failed
Not that I’m aware of