<style>
* {
    font-family: 'MinervaSans';
}

.table {
    display: table;
    width: 200px;
    height: 300px;
    background-color: darkgoldenrod;
}

.row {
    display: table-row;
}

.cell {
    display: table-cell;
}

.a {
    background-color: darkcyan;
    height: 50px;
}

.b {
    background-color: orangered;
    height: 50%;
}
</style>
<div class="table"><div class="row a"><div class="cell">a</div></div><div class="row b"><div class="cell">b</div></div></div>