Allow customers to view and edit the CSS for the Packing Slip HTML
You have some pre-set CSS rules that are used by the Packing Slip HTML template.
Why not allow customers to view and edit these?
That would allow them more ability to customise and structure HTML/CSS properly.
Inserting inline CSS on each element is time-consuming.
Inserting a <style> section at the top of the editor containing some custom classes seems to work, but is a bit of a hack.