* {
  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;
}