p_index.css

@media only screen and (max-width:555px) and (min-width: 380px) {
    .container h1 {
        font-size: 2.5rem;
        margin: 18px;
        padding: 8px 8px;
        margin-top: 38px;
        margin-bottom: 33px;
    }

    #calculation {
        height: 40px;
        width: 350px;
        font-size: 30px;
        padding: 5px 5px;
    }

    .btn {
        width: 80px;
        height: 50px;
        font-size: 22px;
    }

    #row1 {
        margin-top: 34px;
    }

    #row5 {
        margin-bottom: 135px;
    }
}

@media only screen and (max-width:380px) {
    .container h1 {
        font-size: 2rem;
        margin: 16px;
        padding: 6px 6px;
        margin-top: 38px;
        margin-bottom: 33px;
    }

    #calculation {
        height: 40px;
        width: 270px;
        font-size: 30px;
        padding: 5px 5px;
    }

    .btn {
        width: 60px;
        height: 45px;
        font-size: 20px;
    }

    #row1 {
        margin-top: 34px;
    }

    #row5 {
        margin-bottom: 125px;
    }
}