This drupal.org documentation page describes many common pitfalls of Drupal module's CSS: http://drupal.org/node/1887918#pitfalls
To remove these problems, we should follow the best practices guidelines outlined on this drupal.org documentation page: http://drupal.org/node/1887918#best-practices
The work for this issue is being done in the Drupal 8 Mobile Initiative sandbox: http://drupal.org/sandbox/d8-mobile
User interface changes
None. The design objects that style the Drupal module's functionality should be look roughly the same after as they do now.
All of core's modules will have new CSS selectors that better match the design objects being used for their content.
Quite a bit of work has been done in Seven Style Guide sandbox issues, in terms of identifying components and refactoring markup and CSS, but focused on the Seven theme. Contributors are encouraged to take a look at the work done there as a guide to this issue. Some code may be directly portable.
This is one issue in the larger http://drupal.org/sandbox/d8-mobileissue. This issue combines work done in the Drupal 8 Mobile Initiative sandbox: