Measured: across the full width YouTube needs only its seek bar (up to 96 px
from the bottom); the 140 px is the fullscreen button's, at the right end. A
full-width 140 px band handed clicks on the picture to the iframe, which then
takes the keyboard focus and our shortcuts with it. The layer is now two boxes,
hidden from assistive tech (a mouse surface; the keys are its shortcuts), and
the tests render the big view too, where the docked bar sits under the iframe.
peter
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