body {
    background:#111;
    color:#fff;
    font-family:Arial;
    text-align:center;
}

.container {
    display:flex;
    flex-wrap:wrap;
    justify-content:center;
}

.card {
    background:#222;
    margin:10px;
    padding:15px;
    border-radius:10px;
    width:140px;
}

.heatmap {
    display:flex;
    flex-wrap:wrap;
    justify-content:center;
}

.heatbox {
    width:60px;
    height:40px;
    margin:3px;
    display:flex;
    align-items:center;
    justify-content:center;
    font-size:10px;
    border-radius:6px;
}