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

header{
  background-color: antiquewhite;
}

nav{
  background-color: azure;
}
nav > details > ul{
  display: flex;
  flex-direction: column;
}
nav > details > ul > li > a{
  background-color: lightgray;
  display: block;
  text-align: center;
  padding: 10px 20px;
}
nav > details > ul > li > a:hover{
  background-color: darkgray;
}

main{
  background-color: cadetblue;
  height: 400px;
}
main > details{
  background-color: aqua;
  margin: 20px;
  border-radius: 20px;
}
main > details > p{
  padding: 20px;
  border-radius: 20px;
}
main > details > summary{
  background-color: darkgray;
  list-style-type: none;
  display: flex;
  justify-content: space-between;
  padding: 20px;
  border-radius: 20px;
}
main > details[open] > summary{
  background-color: saddlebrown;
}
main > details > summary::after{
  content: "+";
  font-size: x-large;
}
main > details[open] > summary::after{
  content: "-";
  font-size: x-large;
}

footer{
  background-color: wheat;
}