With this css, the checkmarks do appear in the pdf. However, the font used is not even close to the appearance in the screen version of the page. Arial Black would provide the closest looking checkmark to the Google "Open Sans" font, but no matter what fonts and font-families I try I can only get the skinny straight checkmark. Is this a limitation of the fonts installed on your server?
Attachments show the difference in the desired check (curvy & thick) vs. what I'm getting (straight & fine).
wrote on 2016-01-04:
Neither Arial Black nor Helvetica are installed on our servers and so unavailable for PDF. If you require Arial Black or Helvetica in the generated PDF, you can upload the font files via the standard CSS rule. Example: