title: CSS3 animation: blinking overlay box
body: <p>I'd like to create a  element which overlays a part of a page using position: absolute. This  element would be 50% opaque and blink between red and transparent. A bit like what OSX uses (used?) to do for the default button of a dialog.</p>
  
  <p>How to create a infinite animation loop with CSS3?</p>
  
  <p>How to cycle between two background colours in this loop?</p>
  
  <p>Which browsers is possible support today through CSS3 animation?</p>
  
  <p>jQuery animation is an alternative, but I'd like to try CSS3 approach first.</p>