javascript:
/*
	Browser Strobe Light by Relevant
*/
(function(){
document.body.innerHTML="";
document.head.innerHTML="";
var a = document.createElement("style");
a.type="text/css";
a.innerHTML="body.black{background:#000;}body.white{background:#FFF;}";
document.getElementsByTagName("head")[0].appendChild(a);
var a = document.createElement("script");
a.type="text/javascript";
a.innerHTML="var enabled = false;var interval = 500;(function(){var bmp = parseInt(prompt('enter BPM',120));interval = (60/bmp)*1000;})();function toggle(){setTimeout('toggle()',interval);enabled = true;setTimeout('enabled = false;',300);}toggle();var body = document.body;function a(){setTimeout('a()',50);if(!enabled){return true;}body.className = ((body.className == 'black')?'white':'black');}a();";
document.getElementsByTagName("head")[0].appendChild(a);
})();