html, body {
  height: 98%;
}

body {
  display: flex;
  flex-direction: column;
}

header {
  margin: 0 auto;
  width: 100%;
  max-width: 780px;
}

main {
  width: 100%;
  flex: 1 0 auto;
}

nav {
  display: flex;
  align-items: center;
}

footer {
  flex-shrink: 0;
}