style.css

:root {
  --top-color: yellow;
  --bottom-color: lightyellow;
}

html, body {
  height: 100%;
  width: 100%;
  padding: 0;
  margin: 0;
}

.separator {
  background-repeat: no-repeat;
  background-size: 100% 100%;
}

.separator.external {
  background-image: url(source.svg);
}