Images rendering blurry

Site URL: https://caitlin-donahue.squarespace.com/dark-theme

The images are rendering blurry on my site. I have tried everything - they are the correct size, resolution. I have outlined the text, made sure the the ratios are right. I do have some custom css on my site, but it doesn't help if I delete it all either. 

Any advice?? 

I have attached one of the image files here as well