This code from google selector-shell might be useful

/**

• Adds CSS text to the DOM
• @param {string} cssText The css text to add.
• @return {Element} cssNode the added css DOM node.
• @private

*/
SelectorShell.prototype.addCssText_ = function(cssText) {
var cssNode = document.createElement('style');
cssNode.type = 'text/css';
cssNode.id = 'cssh-sheet-' + document.styleSheets.length;

var headEl = document.getElementsByTagName('head')[0];
headEl.appendChild(cssNode);

// IE
if (cssNode.styleSheet) {
cssNode.styleSheet.cssText = cssText;
// W3C
} else {
var cssText = document.createTextNode(cssText);
cssNode.appendChild(cssText);
}

return cssNode;
};