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

header {
    background-color: aliceblue;
}

nav {
    background-color: antiquewhite;
}

nav > details > ul{
    display: flex;
    flex-direction: column;
}

nav>details>ul>li>a{
    display:block;
    padding:20px;
    background-color: lightblue;
    text-align: center;
}

nav>details>ul>li>a:hover{
    background-color: gray;
}

main {
    background-color: lightgreen;
    min-height: 400px;
}

details {
    background-color: cadetblue;
}

details>summary {
    background-color: lightgray;
    list-style-type: none;
    display: flex;
    justify-content: space-between;
}

details>summary::after {
    content: "+";
    font-weight: 700;
    font-size: x-large;
}

details>summary[open]::after {
    content: "-";
    font-weight: 700;
    font-size: x-large;
}

details[open]>summary {
    background-color: cadetblue;
}

footer {
    background-color: beige;
}