It should be.
Look
over here for the specifications concerning CSS used in ePub files.
Especially of interest to you should be the
oeb-page-head and
oeb-page-head values for the
display property.
Also, read this (from that same page):
[6] The content of an element assigned display: oeb-page-head should be presented only as a header, and the content of an element assigned display: oeb-page-foot should be presented only as a footer. Neither should be simply presented as if it were inline or block. Reading Systems, however, are free to present headers and footers either in special areas as usual for paper publications, or to make them available in another way. For example, a device with a small screen might instead pop them up on demand. For purposes of page layout, these display values are similar to block boxes with an absolute position (i.e. a position value of fixed or absolute). That is, they are removed from the normal flow and a new block box is created with its own flow. Margins, padding and other block characteristics are determined as if the element had position: fixed set.
An element assigned display: oeb-page-head or display: oeb-page-foot shall not be considered in effect while any preceding content remains presented. For example, when rendered to a screen with appropriate style settings, the myhead-classed div element below would become the page header as soon as nothing preceding the containing div is displayed:
Code:
<div>
<div class="myhead" style="display: oeb-page-head">
The OEB Publication Structure: Introduction
</div>
<h2>Introduction</h2>
<p>...</p>
</div>
Such a header (or footer) remains in effect until another header (or footer) is in effect instead, or until no part of its parent element remains presented (such as when the div is no longer visible in the above example), whichever occurs first.
Good luck
.