Kosova theme is a simple clean HTML and CSS and is W3C-compliant. It has also some nice usability features. It is compatible with all major browser and even IE6.
Features for the theme include:
- Increase/Decrease font size
- Switch between full and fixed screen
- CSS 3 valid
- Tabbed menu
- Compatible with all major browser
- login block customised
I am working on responsive version of this theme as well as drupal 7. So watch this space!