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Showing and hiding content with pure CSS3 - Opera Developer Community
http://dev.opera.com/articles/view/css3-show-and-hide/

Showing and hiding content with pure CSS3

using :focus pseudo-class

from Opera Developer Community

show/hide without using JS

By http://bit.ly/Tweets2Delicious

Modern websites and applications are more dynamic than old style web pages, with several pieces of well-placed JavaScript providing smoother content updates, more intuitive user feedback and more responsive controls. One very common feature is the expanding/collapsing or shown/hidden box, whether this is a tabbed interface, a content "tray" on the side that can be slid out and then put away again, or a complex tree menu with expanding/collapsing sub-menus. Generally, these features are implemented via JavaScript, however using CSS3 it is possible to create such content using only HTML and CSS — no JavaScript required. In this article I'll show you how this works, including a few examples to get you started.