Steam resolution issue?

Hi, I use a MacBook Pro 13 inch Retina display. I've noticed that if I open the steam downloads within the game that I am unable to click or select anything? I also notice than whenever I reach an achievement this appears on the game in a really small resolution, does anyone know why this is??

Is anybody else familiar with this Mac issue with Steam?

Any help or comments would be great as this is really irritating me!

Thanks in advance.