Hi! If you want to target sepcific elements and have different properties on different breakpoints you can create a class (assign that class to your element) and make use of media queries.
Example
//MY awesome class
.my-class {
font-size: 16px;
//Change the size under tablet
@media screen and (max-width: $breakpoint-md-max) {
font-size: 14px;
//other properties can be here
}
}
More about media queries: Responsive Web Design Media Queries