Add space horizontally between Galleries

http://dev.nataliebork.com/projects/glance/

Notice that there is not space between images on the space row on the mobile view.

Which code do I need to add the the style.css? I reviewed http://www.w3schools.com/css/css_margin.asp but not change.

@media only screen and (max-width: 480px), screen and (max-device-width: 480px), screen and (max-width: 600px)
#gallery-6 .gallery-item {
    padding: 0px 20px;
}
}