Vertical {
    height: 100%;
    width: 100%;
    overflow-x: auto;
}

Placeholder {
    height: 1fr;
    width: 50%;
}

#p1 {
    min-width: 25%;  /* (1)! */
}

#p2 {
    min-width: 75%;
}

#p3 {
    min-width: 100;
}

#p4 {
    min-width: 400h;
}