A Guide To The State Of Print Stylesheets In 2018
▻https://www.smashingmagazine.com/2018/05/print-stylesheets-in-2018
Testing print stylesheets can be something of a bore, typically requiring using print preview or printing to a PDF repeatedly. However, browser DevTools have made this a little easier for us. Both Chrome and Firefox have a way to view the print styles only.
#Firefox : Open the Developer Toolbar then type media emulate print
at the prompt.