body {
  margin: 0;
  height: 100vh;
  background: linear-gradient(-45deg, #1e3c72, #2a5298, #1e3c72, #2a5298);
  background-size: 400% 400%;
  animation: gradientBG 15s ease infinite;
  display: flex;
  justify-content: center;
  align-items: center;
}

@keyframes gradientBG {
  0% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}