table设置tbody滚动条

table tbody {
    display: block;
    height: 400px;
    overflow-y: scroll;
   
}

table thead,
    tbody tr,
    tfoot tr {
    display: table;
    width: 100%;
    height: 40px;
    table-layout: fixed;
    font-size: 16px;
    text-align:center;
 } 
table thead { 
width: calc( 100% - 1em)

}