Default Breakpoints

//screen
@media screen and (min-width: 64.063em) {
...
}
//tablet
@media screen and (min-width:40.625em) and (max-width:64em) {
...
}
//mobile
@media screen and (max-width:48.063em) {
...
}
//phone
@media screen and (max-width:30em) {
...
}

css file location in /themes/master/css/base.css