One surface, switched between panels. Two looks — default and line — and three ways to handle a row of tabs that no longer fits.
The triggers sit in a quiet recess, and a switched panel rises slightly as it appears. That motion is the only thing the seam adds.
The underlined variant, for dividing a page into sections: a line appears beneath the selected label.
A glyph sits beside the label and inherits the trigger's colour. A disabled trigger stays visible and stops accepting presses.
Tabs inside a dialog. Switch between them, then click outside to close.
Reach for this first. The row stays one line and the overflow runs sideways. Only the side with more to come fades, the arrows nudge it along, and a selected tab scrolls itself into view.
Show what fits and park the rest in a More menu — the shape for a screen whose tab count does not change. Picking a hidden item puts its name and glyph on the trigger.
Shrink every unselected tab to its glyph and leave the name to a tooltip. More fits on the line, at the cost of being harder to scan.