Hi @rbiram,
The cause of the proportional space that is being showed in the tooltip, might be due to the fact that there is empty space in the string of the tooltip/column that is used for this function.
Furthermore, HTML is not supported in this tooltip, and I believe styling is being worked on. In the meantime, if you want to add more information to your tooltip, you can use CHAR(13) in your table/view query to add an enter/next line in your tooltip.
I hope this helps for now.
Best regards,
Jochem
@rbiram Styling can most likely also be done in custom.css. We do this in the Maps pop-up for example.