Chrome & Firefox extension for Notion to add 20+ features like sticky outline, small text & full width by default, hide comments & help button, bolder text etc. Download here: https://gourav.io/notion-boost
Right now you can remove top padding and/or change line height.
My biggest issue with Notion is the padding on the sides though. It's really huge.
And especially if I want to have 2 or 3 Notion windows side by side on my screen, the padding eats too much space, and the content inside is squeezed too much, while there is empty white space.
If you manage to create such feature, you can make it only for Pro users.
I tried to make CSS changes myself to achieve removal of the empty sides, but failed. It's bit tricky I guess.