This module comes with a default css stylesheet, which you can disable in the options. Files included for your convinence:
<ul>
<li>views-acordion.css - A default stylesheet with how the classes the author thought would be best used.</li>
<li>views-view-accordion.tpl.php - copy/paste into your theme directory - please the comments in this file for requirements/instructions.</li>
</ul>
Both files are commented to explain how things work. Do read them to speed things up.