How to fit an image inside content-box?

Hi, I need to enlarge only the first image of this page: .col-1
https://verbavolant.altervista.org/category/medioevo/

to fit black box, not red. How can achieve it? I tried:

height: 100%;
width 100%;
padding: 0;
margin: 0;

but has no effect at all.

Thanks in advance