@media (max-width: 600px) {
    .left-bar {
        display: none;
    }
    .main-contents {
        width: 100%;
    }
}
@media (min-width: 601px) and (max-width: 768px){
    .left-bar {
        display: none;
    }
    header{
        justify-content: center;
    }
}

@media (min-width: 769px){
    .menu {
        display: none;
    }
    header{
        justify-content: center;
    }
}