.HolyGrail {
    display: flex;
    min-height: 100vh;
    flex-direction: column;
    background-color: cornsilk;
}
.HolyGrail header,
.HolyGrail footer {
    flex: none;
}

.HolyGrail-body {
    display: flex;
    flex: 1;
    max-width: 100%;
}

.HolyGrail-body nav, .HolyGrail-body aside{
    width: 15%;
}

.HolyGrail-body nav{
    order: -1;
}
.HolyGrail-body main{
    flex: 1;
}