#box1 {
    content-align: left top;
    background: red;
}

#box2 {
    content-align-horizontal: center;
    content-align-vertical: middle;
    background: green;
}

#box3 {
    content-align: right bottom;
    background: blue;
}

Label {
    width: 100%;
    height: 1fr;
    padding: 1;
    color: white;
}