#header{
    display:flex;
    background-color:white;
    height:100px;
    margin:0px;
    justify-content: center;
    align-items: center;
    color:rgba(121, 114, 141, 1);
    font-size: 35px;
    font-weight: bold;
    font-family: arial;
}

    @media screen and (min-width: 300px) and (max-width: 600px) {
        #header{
            height:70px;
            font-size: 25px;
        }
    }