In the screenshot below, I have clicked on the top reaction buttom but not the bottom reaction button.
However, this difference in state is virtually impossible to distinguish - the selected one has the barest of ultradark blue hue if you get your eyes right up to the screen. It would be nice if the selection state was a little more obvious. Thanks!!
Generally I’m loving dark mode, other than the often mentioned items of making changed words in diffs pop out more, and making a ‘dim’ theme option vs the current black.