gistfile1.js

function addIframeStyle(styleUrl) {
	var ss = document.createElement("link");
	ss.type = "text/css";
	ss.rel = "stylesheet";
	ss.href = styleUrl;

	var iframe = document.getElementById('frame_content');
	var idoc = iframe.contentDocument || iframe.contentWindow.document;

	if(document.all) {
		idoc.createStyleSheet(ss.href);
	} else {
		idoc.getElementsByTagName("head")[0].appendChild(ss);
	}
}

addIframeStyle(this.domain + "/css/quizzify_content_shared.css");