Mobile image cropping on 7.1 css

Site URL: https://www.boopdog.co.uk/

Hi guys,

on my home page (7.1) im trying to have it so the image doesnt crop/resize on mobile format but rather just shrinks, staying in the same ratio. Ive tried a few css bits I found around the forum but have not managed to get anything working. 

site is https://www.boopdog.co.uk/ password Boopdog2021*

Thanks 

Add to Design > Custom CSS

@media screen and (max-width:767px) {
body.homepage #page section:first-child {
    min-height: 20vh;
    height: 40vh;
    margin-top: 5vh;
}
}