textual/docs/examples/styles/scrollbar_size2.css

ScrollableContainer {
    width: 1fr;
}

#v1 {
    scrollbar-size: 5 1;
    background: red 20%;
}

#v2 {
    scrollbar-size-vertical: 1;
    background: green 20%;
}

#v3 {
    scrollbar-size-horizontal: 5;
    background: blue 20%;
}