html::before,
html::after {
  background-image: url('theo-schildkroete.png');
  content: '';
  position: fixed;
  width: 100%;
  height: 30px;
  background-size: auto 30px;
  background-repeat: repeat-x;
  filter: drop-shadow(0px 0px 8px rgba(0,0,0,0.8));
  z-index: 1000;
}

html::before {
  top: 0;
}

html::after {
  bottom: 0;
}