How to properly specify font size and face in a classified Ads HTML template?

How to properly specify font size and face in a classified Ads HTML template without html, body and head tags (these tags will be cutted), when template will be put in iframe on page? The classifieds website will use mixed styles which will come partly from it page, so every CSS style I don’t assign specifically, will get a style declaration from main website CSS. I know inline style is a good solution for elements, but sometimes adding styles to a wrapper of template is enough. The sample of html template.