elem {
    width: 100%;
    width: -moz-available;          /* WebKit-based browsers will ignore this. */
    width: -webkit-fill-available;  /* Mozilla-based browsers will ignore this. */
    width: fill-available;
}

elem {
    height: 100%;
    height: -moz-available;          /* WebKit-based browsers will ignore this. */
    height: -webkit-fill-available;  /* Mozilla-based browsers will ignore this. */
    height: fill-available;
}