Hide a section on Mobile

Hi,

I am trying to have a different Color Section for the mobile version of the website. The reason is beacause I would like to use a different background image to be shown on small screens.

so i tried this with no sucess:

@media screen and (min-width: 0px) and (max-width: 400px) {
.fuumi-top { display: none; } /* this is the version for big screens */
}

@media screen and (min-width: 401px) {
.fuumi-top-mobile { display: none; } /* this is the mobile version */
}

is there a way to get around with this?

Many thanks