There is no CSS for the progress bar, the css is generated dynamically by javascript in the webassist/progress_bar/jquery-blockui-formprocessing.js file.
near the bottom is the section that sets the css properties.
the image for the progress abr is set in the HTML using an img tag:
<div id="form1_ProgressMessage" >
<p style="margin:10px; padding:5px;" ><img src="webassist/progress_bar/images/cabo-bar.gif" alt="" title="" style="vertical-align:middle;" /> Please wait</p>
</div>