body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.page-section {
  border: 1px solid red;
  min-height: 120vh;
  transition: background-color 1s;
}

.page-section.active {
  background-color: lightblue;
}