Huh, that's a surprisingly elegant solution to the problem of clothing that works in the face of imprecise manufacturing. The button-hole doesn't have to be exactly the same size as the button and it's okay if no two buttons are exactly the same size as each other, and the fastening method is robust to small departures of the shape from - if this line of thinking is not centrally necessary to sex with Carissa it can wait.
Keltham undoes all the buttons he can see, the motions unpracticed but not too slow; it's obvious enough how a button works, once you see one.
And her shirt lies open before him.
Carissa Sevar is older than any woman he's previously lain with, and prettier than them, in his sight, as nearly as he can tell from just her exposed chest. Carissa being however-many years older than him works for him on a physical level, it seems, so long as he's not at a social power disadvantage to her the way he would have been to a woman that age in dath ilan.
Keltham wonders if there's a non-button trick he's missing for how he could remove Carissa's shirt-sleeves from her arms, without her needing to rise up from her laid-down position; but also Keltham doesn't feel the need to do that right now. The alien clothing on the sexy alien female isn't something he minds.
"I approve," he says a little breathlessly, eyes going between Carissa's face and her chest.