Media Query

Hi there.
On the theme Options page in the Custom CSS box I added a media query for a change to the menu, but the change doesn’t show up on the site. Is there another place I should put media queries?
Here is what I am trying to add:
@media (max-width: 959px) and (min-width: 768px)
.custom_menu #menu, .custom_menu #menu > ul > li > a {
padding: 0px 25px 0px 25px !important;
}
}
Thanks,
Leslie