I don't know if it is the new 3.5 version or the new TwentyTwelve, but I'm trying to build a child theme out of it.
Previously, I remember that in the header.php file I could find the call for the style.css file, and I could have change it in something like
if (is_page_template(..) )
and in this way , I could have loaded a different CSS stylesheet for different templates or pages.
whereas now, trying to study the TwentyTwelve theme, I don't see anything like this in the header.php
The call for the stylesheet is inside wp_head() instead.
in this way I don't know how to say "no don't load the style.css but for this page load style_2.css"