@media only screen and (max-width: 800px){
    nav ul{
        position: absolute;
        top: 70px;
        left: 0;
        background: #333;
        width: 100%;
        overflow: hidden;
        transition: max-height 0.5s;
    }
    nav ul li{
        display: block;
        margin-right: 50px;
        margin-top: 10px;
        margin-bottom: 10px;
    }
    nav ul li a{
        color: #fff;
    }
    .menu-icon{
        display: block;
        cursor: pointer;
    }
}
@media only screen and (max-width: 600px){
    .row{
        text-align: center;
    }
    .col-2, .col-3, .col-4{
        flex-basis: 100%;
    }
}