Choosing Graybird in Appearance/Style makes panel dark without any obvious way of going back to default

Originally both 'Graybird' and 'Graybird-dark' choices were unselected. Once I selected one of them - panel switched to the dark background and there is no obvious way to unselect the style.

Is the 'Default' item missing there? It looks like there should be a 'Default' selection that would switch to default.