Tracking UI interactions
with CSS

(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');

ga('create', '......', '......');
ga('send', 'pageview');
ga('send', 'event', 'ui-interaction', 'click', 'link clicked', 1);
When all this information is collected, it is sent to the Analytics servers in the form of a long list of parameters attached to a single-pixel GIF image request.
new Image().src = '/stats.gif?' + parameters
background-image: url('http://www.google...');
input[type="button"]:active {
    background-image: url('http://www.google...');
}
input[name="message"]:focus {
    background-image: url('http://www.google...');
}
input[value="female"]:checked {
    background-image: url('http://www.google...');
}
@media all and (max-width: 640px) {
    body {
        background-image: url('http://www.google...');
    }
}