* {
    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: lightgray;
  text-align: center;
}
nav>details>ul>li>a:hover{
  background-color: gray;
}
main{
  background-color:rgb(136, 216, 136);
  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: 500;
}
details[open]>summary::after{
  content: "–";
  font-size: x-large;
  font-weight: 500;
}
details[open]>summary{
  background-color: cadetblue;
}
footer{
  background-color:beige;
}