Involved files: functions.php
WordPress Codex writes about this:
The child theme’s stylesheet will overwrite the parent theme’s stylesheet, but chances are you want to include the parent theme's stylesheet. To do this, you need to start the stylesheet with the following line:
This line must go after the header code and before any other CSS rules. If you put other CSS rules before the @import, it will not work.
2012-XTended WordPress theme encompass all the best features of the default WordPress themes in one place, plus more usability and code improvements! Do you like elegant mobile-first HTML5 ready structure of Twenty Twelve and custom per-post headers from Twenty Ten? What about three footer widgets from Twenty Eleven and icon webfont support from Twenty Thirteen? It's all there, you don't have to make difficult compromises, you have everything in one neat package
2012-XTended WordPress theme is a child theme created for the default theme Twenty Twelve to be used as a learning tool or your own little web development "framework". It helps to understand how to extend parent themes and build your own child themes, hacking them the way you want it. You get the best coding examples from default WordPress themes and the best hacks from the child theme ...continue reading
When I first saw new default WordPress theme Twenty Thirteen, I really liked new addition for style.css - a Table of Contents. Default theme should help new users to understand where goes what and especially it is useful when developing child themes. Table of Contents for style file helps to achieve this task, I even think that it would be useful to have Table of Contents for functions.php too ...continue reading