Drupal 8 includes several new theming principles and improvements to enhance the user experience and make the platform more mobile friendly and modern, including a responsive base theme, CSS improvements, improved aggregation, in-place field editing, dropped IE6-7 support, TWIG as the new templating language, and various new field types and modules in core.

1. Theming principles
in Drupal 8
Kirill Cebotari (oresh)

2. Mobile friendly

3. Drupal is now a REST
server with a CMS on top

4. New design

5. New Seven admin theme

6. UX improvements

7. Responsive base theme
out of the box

8. Breakpoint module in Core

10. CSS3
instead
of JavaScript

11. In-place editing for Fields

12. Better aggregation with
CSS weights

13. Frontend
Automated
Testing

14. IE6-7 support dropped

15. Partially dropped
IE8 Support

16. .theme and .yml
files in theme

17. .yml CSS
override &
remove

18. TWIG!

19. #DreamMarkup

20. jQuery 1.9 &
jQuery UI 1.10.2

21. Tour module

22. WYSIWYG
in core

23. Fieldable custom blocks

24. New CSS Architecture

25. .button class for
all buttons and links

26. Primary
button type
added

27. CSS/JS Libraries

28. Normalize.css

29. Modernizr + client-side
feature detection

30. New Toolbar

31. Footer menu by default

32. Theme individual layouts

33. New field types:
E-mail, Link/URL, Phone
number, Date/Time and
Entity Reference

34. Responsive table classes

35. Browser targeted
drupal_add_js()