CSS3 Animation: Blinking Overlay Box

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

Solution 1:

The first 2 questions are answered by the spec.

To loop: animation-iteration-count: infinite;

And cycling the background color involves specifying a @keyframes rule.

body { background: #0ff; }

@-webkit-keyframes blink {
    0% { background: rgba(255,0,0,0.5); }
    50% { background: rgba(255,0,0,0); }
    100% { background: rgba(255,0,0,0.5); }
}

@keyframes blink {
    0% { background: rgba(255,0,0,0.5); }
    50% { background: rgba(255,0,0,0); }
    100% { background: rgba(255,0,0,0.5); }
}

#animate { 
    height: 100px; 
    width: 100px;
    background: rgba(255,0,0,1);
}

#animate {
    -webkit-animation-direction: normal;
    -webkit-animation-duration: 5s;
    -webkit-animation-iteration-count: infinite;
    -webkit-animation-name: blink;
    -webkit-animation-timing-function: ease;   

    animation-direction: normal;
    animation-duration: 5s;
    animation-iteration-count: infinite;
    animation-name: blink;
    animation-timing-function: ease;       
}

(don't forget any applicable vendor prefixes!)

As far as browser support goes, i couldn't tell you specifics, but in any case i would recommend feature detect via modernizr and a javascript fallback.

Here is an example that works in webkit and fulfills at least some of your requirements. NOTE: I don't use a mac so i wasn't sure the specifics of the effect you referenced.

Solution 2:

Once you've set the animation up in the stylesheet (-webkit-transition:), you can simply change the color with JavaScript.

function toggleColor(element)
{
    var red = "rgba(255,0,0,0.5)";
    var transparent = "rgba(255,0,0,0)";
    element.style.backgroundColor = ((element.style.backgroundColor == red) ? transparent : red);
    window.setTimeout(function()
    {
        toggleColor(element);
    });
}

Currently, only Webkit browsers (Safari & Chrome) support CSS-Animations.