*{
    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{
  display: block;
  padding: 20px;
  background-color: lightgray;
  text-align: center;
}

nav > details > ul > li{
  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-weight: 700px;
  font-size: x-large;
}

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

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

footer{
  background-color: beige;
}