Keeps the user control bar overlayed on top of the video area instead of reserving a dedicated area below it. This avoids layout height changes when showing/hiding controls.
Useful for tight layouts where vertical space is limited, or when combined with widgets/iframes.
Related behavior: &controlbarspace forces a dedicated space for the control bar. Do not use both together.
Mobile: behavior may vary depending on screen height; overlay avoids shrinking the grid area when controls appear.
