html {
  height: 100%;
}
body {
  margin: 0;
  padding: 0;
  min-height: 100%;
  display: grid;
  grid-template-rows: 1fr auto;
}
header {
  width: 100%;
}
footer {
  grid-row-start: 2;
  grid-row-end: 3;
  width: 100%;
}