header {
  padding-top: 50px;
  height: 25px;
  background-color: orange;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
}

main {
  margin-top: 150px;
  margin-bottom: 150px;
  overflow-y: auto;
  height: calc(100vh - 150px - 150px);
}

footer {
  height: calc(75px + env(safe-area-inset-bottom));
  background-color: darkgreen;
  position: fixed;
  bottom: 0;
  left: 0;
  width: 100%;
}