*{
    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: lightgrey;
  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-weight: 700;
  font-size: x-large;
}
details[open]>summary::after{
  content:"–";
  font-weight: 700;
  font-size: x-large;
}
details[open]>summary{
  background-color: cadetblue;
}
footer{
  background-color: beige;
}