This says the dismissable button is a "ghost button, placed in the top right corner" (BTW a link to the ghost buttons may be useful).
So there it does specify the hovered, etc. colors only for grey. I doubt that this is how it should look on a yellow or red message bar.
So how should it actually look? May we even just use the same colors as other buttons? (except that the dismissable button should be transparent when not hovered/in the "default" state.)
This says the dismissable button is a "ghost button, placed in the top right corner" (BTW a link to the ghost buttons may be useful).
So there it does specify the hovered, etc. colors only for grey. I doubt that this is how it should look on a yellow or red message bar.
So how should it actually look? May we even just use the same colors as other buttons? (except that the dismissable button should be transparent when not hovered/in the "default" state.)