.first-level{
    background-color: #ffffff;
}
.second-level{
    background-color: rgba(192,192,192, 0.1);
}
.third-level{
    background-color: rgba(192,192,192, 0.15);
}
.fourth-level{
    background-color: rgba(192,192,192, 0.25);
}
.fifth-level{
    background-color: rgba(192,192,192, 0.4);
}

.first-level td,
.second-level td,
.third-level td,
.fourth-level td{
    vertical-align: middle;
}