var styleElement = document.createElement('style');
styleElement.type = 'text/css';
if (styleElement.styleSheet) {
  styleElement.styleSheet.cssText = 'div.products .box{display:none;}';
} else {
  styleElement.appendChild(document.createTextNode('div.products .box{display:none;}'));
}
document.getElementsByTagName('head')[0].appendChild(styleElement);