没啥说的，直接上代码

export default class CssUtil {
    static addCssCode(parentNode,code){
        let style = parentNode.getElementsByTagName('style')[0]
        if(!style){
            style = document.createElement('style')
            style.type = 'text/css'
            style.rel = 'stylesheet'
            parentNode.insertBefore(style,parentNode.firstChild)
        }
        //for Chrome Firefox Opera Safari
        style.appendChild(document.createTextNode(code));
    }
}