position_example2.css

html {
  background: #b3b3b3;
  padding: 15px;
  border: 5px solid white;
  margin: 15px;
  height: 2000px;
}

body {
  background: #fa923f;
  padding: 20px;
  border: 5px solid black;
  margin: 0;
}

.parent {
  background: white;
  padding: 20px;
  border: 5px solid black;
  margin: 10px;
}

.parent .country {
  background: #fa923f;
  color: white;
  padding: 10px;
  border: 5px solid black;
  margin: 10px;
  position: sticky;
  top: 20px;
}

.parent .cities {
  background: rgb(105, 105, 109);
  color: white;
  padding: 10px;
  border: 5px solid black;
  margin: 10px;
}