Theme Engine Documentation

Yes. In your layouts and stylesheets any version of HTML and CSS will do the job. You can go with the newest HTML 5 semantics and columns, or choose regular block type DIVs, or go retro with the '90s style in tables - anything will work fine.

ContentAir uses the newest HTML5 methods in the administration area, but the public side is in HTML4. To preserve the browser compatibility, system-generated HTML uses only block type DIVs with regular box sizing in layout building. Except for source code semantics, this does not create any limitations for you and guarantees that your website is displayed properly for all visitors.