body{
  height: 400vh;
}
header{
  height: 80px;
  background: pink;
}
nav{
  padding: 10px;
  background: lightblue;
  position: sticky;
  top:0;
}
.container{
  height: 200vh;
  background: #ccc;
}
footer{
  background: lightgreen;
  padding:10px;
}