I just thought I'd post this in hopes of saving someone else a couple of hours of frustration and digging for a solution.
When you use a shortcode to display a ToDo list on a page or post, make sure you don't accidentally paste the shortcode into the Visual editor as preformatted text. If you do, the ToDo list will ignore the theme stylesheets and will appear poorly formatted in ugly Courier font.
If you have this problem, look at the page or post in HTML view and make sure the shortcode isn't surrounded in ` tags.
(This applies to all plugin shortcodes, not just Cleverness ToDo List.)
Cleverness ToDo List is awesome! Thanks so much!