<style>

/*设置 tbody高度大于400px时 出现滚动条*/

    table tbody {

        display: block;

        height: 400px;

        overflow-y: scroll;

    }

    table thead, tbody tr {

        display: table;

        width: 100%;

        table-layout: fixed;

    }

/*滚动条默认宽度是16px 将thead的宽度减16px*/

    table thead {

        width: calc( 100% - 1em);

    }

</style>