Have you updated to the latest Obsidian that just came out? PDF font issues should have been fixed.
A snippet would also work but we need to be specific:
Title ← h1(?) # Title red
Something normal ← no change
Something bold ← bold text in red
Something italic ← italic text in light blue (do you know the color hex?)
Something highlighted ← as you are using a dark theme, this one won’t translate well to a PDF. maybe something other than the default yellow?