I know of no ePUB reader that supports oeb-page-head (or foot), although it would be the proper way to create running headers.
But, anyway, if you are using a class, you need not specify a style, i.e., you should do:
Code:
<div class="myhead">
The OEB Publication Structure: Introduction
</div>
and, in the CSS:
Code:
div.myhead { display: oeb-page-head }
(but it won't work, as I said).