Transitions, Transforms and :Target
Off Canvas Menus with CSS3 Transitions and Transforms, by Nicolas Cerminara. As states the author, Off canvas menus are living outside the viewport. In this column, the author shows one simple solution for achieving this result. Explanation, demo and code. This is not exactly "an animation". However, this style of menu brings a dynamic in a web page.
Off Canvas Menu with CSS :target, by Chris Coyier. The authors offers a CSS only solution, and full working examples. This article was published in 2012.