How would I override misc/ui/jquery.ui.theme.css
I don't have enough rep to add comments, but here is my two cents. In addition to Clive's comment, take a look at the weight and group option being used in drupal_add_css, in views_accordion.module. You can implement your own stylesheet here and assign a CSS_THEME for its group and a larger weight number than that of views_accordion, which I'm pretty sure would have used CSS_DEFAULT instead. Here are the docs page. drupal_add_css