:root {
  --footer-height: 40px;
}

html {
  position: relative;
  min-height: 100%;
}

body {
  /* Margin bottom by footer height */
  margin-bottom: var(--footer-height);
}

footer {
  position: absolute;
  bottom: 0;
  width: 100%;
  height: var(--footer-height);
}