@media only screen and (max-width: 568px) {
    #intro {
        padding: 0 0px;
    }

    h1 {
        font-size: 40px;
    }

        h1::after {
            height: 30px;
        }

    p {
        font-size: 18px;
    }

    .btn {
        font-size: 16px;
    }
}

@media only screen and (max-width: 320px) {
    h1 {
        font-size: 28px;
    }

        h1::after {
            height: 4px;
        }
}