Print-Pro-Matic allows loading in an external css file for the print view, rather than have to manually entered all definitions in to the Custom CSS area.
For example, this should load in a css file that gives the target element a lovely purpley dotted border:
[print-me css_url="http://spacedonkey.de/wp-content/uploads/2015/07/purpeat.css" target=".purpeoeater"]
Flyin’ Purple People Eater
Well, bless my soul rock ‘n roll flying’ purple people eater
Pigeon-toed under-growed flyin’ purple people eater
One-eyed one-horned it was a people eater
What a sight to see!