@media (max-width: 960px) {
    .box {
        background: blue;
    }
    .box p::after {
        content: "960px";
    }
}

@media (max-width: 768px) {
    .box {
        background: green;
    }
    .box p::after {
        content: "768px";
    }
}

@media (max-width: 480px) {
    .box {
        background: orange;
    }
    .box p::after {
        content: "480px";
    }
}