body {
  margin: 0;
  height: 100vh;
  display: flex;
  flex-direction: column;
}

h1 {
  flex: 1;                 /* ocupa o espaço disponível */
  display: flex;
  justify-content: center; /* centra horizontal */
  align-items: center;     /* centra vertical */
  text-align: center;
}

footer {
  text-align: center;
  padding: 5px;
}