*{
    padding: 0px;
    margin: 0px;
    box-sizing: border-box;
}

header{
    background-color: cornflowerblue;
    height: 200px;
    text-align: center;
}
nav{
    background-color: lightgreen;
}

nav>ul{
    display: flex;
    flex-direction: column;
    gap: 3px;
    list-style-type: none;
}

nav>ul>li>a{
    display: block;
    background-color: aqua;
    padding: 10px 0px ;
    text-align: center;
}

main{
    background-color: lightpink;
    height: 400px;
    padding: 20px;
}

footer{
    background-color: lightyellow;
    padding: 20px;
}

@media screen and (min-width: 399px){
    nav>ul{
        flex-direction: row;
        justify-content: center;
        gap: 30px;
    }
}