Max image size on mobile view?

Site URL: https://saffron-snail-5gar.squarespace.com/

Hi, 

I'm using white png images as supporting graphics on my site. On the desktop version they are set to appear small using various spacers but on mobile they span full width. Is there a way to set a max size on mobile so I can reflect the desktop version?

pass: prefir1

Thanks!

Add to Design > Custom CSS

@media screen and (max-width:767px) {
/* arrow */
div#block-af7714ea96ec95074f03 {
    width: 30%;
}
/* trees */
div#block-3891780a1011b77e916e {
    width: 30%;
}
}