html {
  height: 150vh;
  background: #39ca74;
}
.bottom {
  background: #39ca74;
  position: fixed;
  height: 50vh;
  top: 0;
  left: 0;
  right: 0;
}
.top {
  padding-top: 50vh;
  height: 50vh;
  background: #3a99d8;
}