input 的 placeholder 样式修改

        input::-webkit-input-placeholder{
            color:#999999;
        }
        input::-moz-placeholder{   /* Mozilla Firefox 19+ */
            color:#999999;
        }
        input:-moz-placeholder{    /* Mozilla Firefox 4 to 18 */
            color:#999999;
        }
        input:-ms-input-placeholder{  /* Internet Explorer 10-11 */ 
            color:#999999;
        }