header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background-color: white; /* or your background */
}

/* Don't add padding here unless you manually need it */
body {
  margin: 0;
}

/* Add spacing using a dedicated spacer if needed */
main {
  padding-top: 80px; /* use the actual height of your header */
}