Responsive image grid

Hello,

is it possible to make the image galery on homepage to be a responsive image grid? I am very happy with the theme, but I need the images to be fully displayed, the images in portrait-style to be displayed this way and the images to wrap when the screensize is changing. I tried adapting the css according to the instructions found on w3school (Responsive Image Grid), but it did not help. This is what I have to far:

.site-main {
	display:flex;
	flex-wrap: wrap;
}
.acme-col-3 {
	flex: 33.33%;
	max-width: 33.33%;
	padding: 0 4px;
	
}
.masonry-item.post-item {
	background-position: center center;
	background-repeat: no-repeat;
	background-size: contain;
}

It would be great if someone could share an idea how to do it.

The page I need help with: [log in to see the link]