<div>test</div>
div {
  width: 10rem;
  height: 10rem;
  border: 5px solid gray;
}

@media (prefers-color-scheme: dark) {
  div {
    background: black;
    color: white;
  }
}

@media (prefers-color-scheme: light) {
  div {
    background: white;
    color: black;
  }
}

External CSS

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External JavaScript

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