<p>
  If you're using inverted colors, this text should be blue on white (the
  inverse of yellow on black). If you're not, it should be red on light gray.
</p>
<p>
  If the text is gray, your browser doesn't support the `inverted-colors` media
  feature.
</p>

p {
  color: gray;
}

@media (inverted-colors: inverted) {
  p {
    background: black;
    color: yellow;
  }
}

@media (inverted-colors: none) {
  p {
    background: #eee;
    color: red;
  }
}