Originally Posted by DSpider
Try using SVG instead of styling it in CSS - which some e-readers could very well ignore. Create those frames in Inkscape, add the text, and add them to the ePub.
IMHO, this is a bad idea. SVG images containing text are treated like any other image. I.e. they cannot be searched and they won't resize if the text is resized.
And SVG images of just the box are also no solution, because superimposed text is often displayed differently by different readers.
Just forget about Calibre and focus on ADE and iBooks compatibility, because those who use Calibre as their main ebook reader most likely won't have the money to buy your client's books anyway.