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


main {
    background-color: green;
    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-size: x-large;
    font-weight: 700;

}

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

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

footer {
    background-color: beige;
}