Original Image Size

Hello!
The map is used for the mobile version.
Exactly the same map i took for the desktop version with different features.

In the mobile version the sight is ok, but on desktop its confusing that there are 2 similar maps.
So i want to display the map in original size, in my case 480-320, so its smaller as the desktopversion.
I tried to edit the css, but its displayed as inactiv, seems the changes in css doesnt work.

This lines in CSS:
.imgmap-frontend-image img, .imgmap-frontend-image canvas {
/*
max-width: 100% !important;
width: 100%;
*/
height: auto; }

I use the newest version of imagemapper.

Thanks a lot!

https://wordpress.org/plugins/imagemapper/