Function build_scene 

pub fn build_scene<'a>(
    children: &'a [ChildComponent],
    viewport: (f32, f32),
) -> BuiltScene<'a>

Build a box tree for a flat list of scene-level children at a given viewport size.

The implicit scene root is a display: flex; flex-direction: column; width/height: 100%; children flow vertically unless they specify position: { x, y }, in which case they become position: absolute.