Theme the progress bar when in batch API with AJAX I am looking to create a stylized theme for the progress bar for the batch API screen. I wish to alter the HTML and CSS being displayed in order to do so.

I know how to add the CSS to the page. I am aware of the hook theme_progress_bar, but according to the documentation "Note that the core Batch API uses this only for non-JavaScript batch jobs.".

What is the best method for overriding the HTML for AJAX driven batch API jobs?
Ultimately decided to use the hook hook_js_alter() in order to replace misc/progress.js with my own version. You can declare your own markup in this file, and also react on progress update (every 1500 ms out of the box).

In case anyone was wondering, this is the outcome of this http://drupal.org/project/nyan