A basic HTML file should look like this:
<!doctype html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- The page supports both dark and light color schemes,
and the page author prefers / default is light. -->
<meta name="color-scheme" content="light dark">
<!-- Replace the Bootstrap CSS with the
Bootstrap-Dark Variant CSS -->
<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap-dark.min.css" rel="stylesheet">
<title>Hello, world!</title>
<!-- Optional Meta Theme Color is also supported on Safari and Chrome -->
<meta name="theme-color" content="#111111" media="(prefers-color-scheme: light)">
<meta name="theme-color" content="#eeeeee" media="(prefers-color-scheme: dark)">
</head>
<body>
<!-- ////////////// -->
<!-- Your HTML here -->
<!-- \\\\\\\\\\\\\\ -->
<!-- Optional Bootstrap JavaScript -->
<script src="location/of/the/bootstrap.js/here"></script>
</body>
</html>That's all. The page will automatically transition to Dark Mode when the users sets their OS (or Firefox theme) to Dark Mode.
Refer to the Bootstrap 5 Docs for more help.