Feel free to use these designs or make your own then post
Here's some ideas to get you started. or make your own and share your designs on steemit.
These backgrounds are royalty free 'labeled for reuse' in google search.
To find backgrounds yourself just do a google image search for 'christmas' or 'christmas cards' and select 'tools'
(under google search bar to the right) then select 'usage rights' and then 'labeled for reuse'
Once you've got your image you can then add text in photoshop or word or another DTP program.
Most programs have templates for postcards, cards etc.
if any body needs any help getting started, post your question in a comment here and ill point you in the right direction.
here's a link to a font similar to steemit. Netto Free TrueType Font Download - ufonts.com
http://ufonts.com/fonts/netto.html