How can I change the length/height of the background image

Hey,
I already tried:

@media only screen and (max-width: 640px) {#collection-61d720afc51e9c7b1d735235 {height: 20px}}

but it didn't work.

2 hours ago, HM_S-S said:

Hey,
I already tried:

@media only screen and (max-width: 640px) {#collection-61d720afc51e9c7b1d735235 {height: 20px}}

but it didn't work.

Can you share your site with the protected password?