I once looked at an online conversion tool I think it was called Fusion. Can't find anymore.
If anyone has 'best practice' or 'best tool' recommendations to do this then please offer.
In this case I'm going to be pasting the resulting code into CIVI's Bulk Mailer tool which adds a level of complexity (blocks) because it can switch from WSYIWYG to "Source" mode (HTML/CSS code) edit modes. CIVI seems to have its own preview ideas that aren't shared by the browsers I'm testing my code in and in Coda 2.5 the IDE I use.