*{
    padding: 0px;
    margin: 0px;
    box-sizing: border-box;
}

header{
  background-color: aliceblue;
}

nav{
  background-color: antiquewhite;
}

nav > ul{
  display: flex;
  flex-direction: column;
}

nav > ul > li > A{
  padding: 20px;
  background-color: lightgrey;
  text-align: center;
  display: block;
}

main{
  background-color: darkgreen;
  min-height: 400px;
}
details{
  background-color: cadetblue;
}

details > summary{
  background-color: lightgrey;
  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;
}