This page shows how to override browser's default styling in dark mode. No JS needed. 

@media (prefers-color-scheme: dark) {
  h2.dark {
    color: #bae6fd; /* override the default dark mode text color white (#fff) */
  }
}

An h2 tag with browser's default color

An h2 tag with prefers-color-scheme override

Some text with custom background-color override.

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