There's a lot that goes into developing a custom responsive theme. Learn to how use Compass, SASS and the Foundation framework to simplify theming.
Just as Drupal uses php and a database to output html, theming frameworks use Compass and SASS to output css. What's the benefit? How about something like:
You can create variables, mixins and functions. You can nest selectors. Keep theming elements organized in a logical way (views theming in _views.scss; block theming in _block.scss).
Frameworks like Aurora and Zurb Foundation give your theme a powerful head start, including grids and many theme variables and functions.
- Installing Compass
- Starting a Foundation 'project' (that's the beginning of your new theme)
- Defining variables, mixins and functions
- SASS basics: structure, nesting and compiling
- How to turn a one column panels layout into a complex grid layout with just a couple lines of code
- Using Foundation's built-in media queries to make your site responsive
- .gitignore / deployment considerations