How to prevent auto scaling of galleries?

Hello,

I had a recent problem with squarespace auto scaling my images up resulting in pixelated images. I had all images in my galleries saved and uploaded at 720px however in the galleries pages (Minsk) they are being upscaled fro some reason.

I tried using the css

.image-stack .image-wrapper img { width: auto; max-width: 100%; }

which seemed to work (although created a large gap between the bottom of the image and the progress indication dots), however even this has now stopped working. Is anyone able to solve this?

On a side not, is there some custom code for ensuring gallery images are centred in the page? Thought I would ask here rather than open a new question.

Thanks