Thumbnails cropping

Hi. Is there a way to have thumbnails resize rather than crop? I have them set at 300×300 but some of the images are portrait and some landscape, so it often crops too much of the image off. Is there some CSS I can add perhaps?

Also, is there a way to change the thumbnail size for specific galleries ON MOBILE ONLY?

I tried this CSS, but it doesn’t work. (Don’t laugh at my coding)!

@media screen only and (max-width: 600px) {#foogallery-gallery-1888 {
thumbnail-height: 500px;
} }

Thanks for your help