Demo of responsive template with mixins.

style.less

// Rename:
// .locu-mobile-menu => .mobile-mixin
// .locu-web-menu    => .web-mixin
// Then, use the mixins like so

@media screen and (max-width: 480px) {
  .mobile-mixin;
}

// Keep this if you want the mobile preview to show your small-screen style
.locu-mobile-menu {
  .mobile-mixin;
}

@media screen and (min-width: 481px) {
  .web-mixin;
}