You mean like a decorating theme? Hopefully you aren't thinking like unicorns or Alice in Wonderland. If you are partial to something along these lines it's OK to pay it homage it in a small way like maybe on your engraved napkins as one would a monogram. Otherwise keep it elegantly simple. Regardless if you choose the Ritz Carlton or Farmer John's Barn as your venue. Leave the “themes” to the kids birthday parties. The exception being of course if you're date is near Christmas or on New Year's Eve. You may tastefully acknowledge the season without going overboard. ie: Santa as your officiant=NOT!