main a {
  color: blue;
}

html,
body {
  height: 100%;
}
body {
  display: flex;
  flex-direction: column;
}

main {
  flex: 1 0 auto;
}
.footer {
  flex-shrink: 0;
}

iframe {
  width: 100%;
  min-height: 300px;
  border: none;
}