Instructions for how to do this for version 0.11 can be found at the Trac site, here's an example from that page that adds custom CSS as well as a header and a footer.
Say you want to add a link to a custom
stylesheet, and then your own header
and footer. Create a file
/path/to/env/templates/site.html or
/path/to/inherit/option/templates_dir/site.html,
with contents like this:
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:py="http://genshi.edgewall.org/"
py:strip="">
<!--! Add site-specific style sheet -->
<head py:match="head" py:attrs="select('@*')">
${select('*')}
<link rel="stylesheet" type="text/css"
href="${href.chrome('site/style.css')}" />
</head>
<body py:match="body" py:attrs="select('@*')">
<!--! Add site-specific header -->
<div id="siteheader">
<!--! Place your header content here... -->
</div>
${select('*|text()')}
<!--! Add site-specific footer -->
<div id="sitefooter">
<!--! Place your footer content here... -->
</div>
</body>
</html>