I think part of that is an illusion, since for something bowing upwards, the usualy anchor point of top left seems rotated clockwise. But there is still a real

I think part of that is an illusion, since for something bowing upwards, the usualy anchor point of top left seems rotated clockwise. But there is still a real rotation - look at wyoming or colorado for a perfect rectangle. My guess is the div element isn't quite centered - perhaps too much padding on the right edge, causing the center point to be off to the right. So when it bows you get the rotation bias