Brief flash of buttons when closing

[jools-r]

This could be specific to my layout but I'm seeing a brief flash of the buttons on closing. It seems to occur at the point where @.is-closing@ is removed from the dialog, though it's very hard to tell in the dev tools.

On a hunch, I added &:not([open]) to the classes that set the buttons to zero opacity around

Parvus/src/scss/parvus.scss

Lines 286 to 287 in 1fd9a32

	&--is-opening,
	&--is-closing {

of the scss and it seems to have helped.

&:not([open]),
&--is-opening,
&--is-closing {

Could I potentially be causing myself problems with this?