min-height.css

/* Mobile */
@media (min-width:320px) { 

    .tester {
        width:100%;
        height:500px;
        background-color:white;
    }
}

/* Tablet */
@media (min-width:640px) {

    .tester {
        width:100%;
        height:500px;
        background-color:red;
    }   

}

/* Desktop */
@media (min-width:960px) {

    .tester {
        width:100%;
        height:500px;
        background-color:blue;
    }   

}