vmax
One percent of the larger side — the unit that embraces overflow.
One vmax is 1% of the viewport's larger dimension — the exact mirror of vmin, and the reason it is so much less seen: where its sibling guarantees fitting, this one guarantees spilling. On a portrait screen it measures by the height; on landscape, by the width.
It is the right choice when excess is the point: a backdrop that covers the window however it is turned, a texture that may leave no gap, a cover's breathing room that follows the device's long side.
.pano {
height: 8vmax;
}