通过css3修改input的placeholder颜色

        input::-webkit-input-placeholder, textarea::-webkit-input-placeholder {
            /* WebKit browsers */
            color: grey;
        }
        input:-moz-placeholder, textarea:-moz-placeholder {
            /* Mozilla Firefox 4 to 18 */
            color: grey;
        }
        input::-moz-placeholder, textarea::-moz-placeholder {
            /* Mozilla Firefox 19+ */
            color: grey;
        }
        input:-ms-input-placeholder, textarea:-ms-input-placeholder {
            /* Internet Explorer 10+ */
            color: grey;
        }