Borrowing from Android, allows you to use the device-independant pixel unit (dp) in CSS stylesheets.

dp.js

(function(){
	var dpi;

	function get_dpi(){
		var div = document.createElement("div");
		div.style.visibility = "hidden";
		div.style.width = "1in";
		div = document.body.appendChild(div);
		var dpi = div.clientWidth;
		div.parentElement.removeChild(div);
		return dpi;
	}

	function parse(style){
		return style.replace(/[0-9]+(?:dp)(?=\W)/g, function(match){
			var dp = parseInt(match);
			return dp * (dpi / 160) + "px";
		});
	}

	function init(){
		dpi = get_dpi();

		var stylesheets = document.styleSheets;
		for (var i = stylesheets.length - 1; i >= 0; i--) {
			stylesheets[i].ownerNode.innerHTML = parse(stylesheets[i].ownerNode.innerHTML);
		};
	}

	window.addEventListener("DOMContentLoaded", init, false);
})();