body {
  margin: 0;
  padding: 0;
  height: 100vh;
  overflow-y: auto;
}

main {
  position: relative;
  height: 100vh;
  overflow: hidden;
}

section.panel {
  position: absolute;
  height: 100vh;
  width: 100%;
  top: 0;
  left: 0;
  padding: 1rem;
}
section.panel:not(:first-child) {
  top: 100%;
}