.tableFixHead {
    height: 30em;
}
table {
    display: flex;
    flex-flow: column;
    height: 100%;
    width: 96%;
}

table tbody {
    /* body takes all the remaining available space */
    flex: 1 1 auto;
    display: block;
    overflow-y: scroll;
}
table tbody tr {
    width: 100%;
}
table thead,
table tbody tr {
    display: table;
    table-layout: fixed;
    font-size: 1.0vw;
}

table thead {
    /* head takes the height it requires,
    and it's not scaled when table is resized */
    flex: 0 0 auto;
    width: calc(100% - 0.9em);
    font-size: 0.9vw;
}