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HTML

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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <main>
  <h1>Style queries with variable values</h1>
  <p>
    We can reference
    custom properties using <code>var()</code>
    inside
    <a href="https://drafts.csswg.org/css-contain-3/#style-container">style queries</a>.
    That means, for example,
    we can query if the <code>background-color</code>
    on the container
    is currently <code>var(--bg-light)</code> or
    <code>var(--bg-dark)</code>.
    Open up DevTools and toggle the light/dark mode
    paintbrush to see it work.
  </p>
  <p>
    Currently this demo requires
    Chrome/Edge 107+ with
    experimental-web-platform-features enabled
    in <code>about://flags</code>,
    as well as
    an extra <code>--background-color</code>
    variable to query, since the Chrome prototype
    does not support querying normal properties.
  </p>
  <pre><code>
@container theme style(--background-color: var(--bg-dark)) {
  /* styles for our dark theme */
}

@container theme style(--background-color: var(--bg-light)) {
  /* styles for our light theme */
}
</code></pre>
</main>
<footer>
  <p>
    This footer section uses a style query
    to apply the opposite of the root theme.
    You can tell it's a footer,
    because it includes my name with a link:
    <a href="https://miriamsuzanne.com">Miriam Suzanne</a>
  </p>
</footer>
!

CSS 

              
                /* 
Currently the Chrome prototype
only allows us to query custom props,
so we use an extra `--background-color` variable.
For the ideal but unsupported solution see:
https://codepen.io/miriamsuzanne/pen/ExRvRrr
*/

html {
  --bg-dark: mediumvioletred;
  --bg-light: snow;
  --background-color: var(--bg-light);
  color: black;
}

html,
footer {
  background-color: var(--background-color);
  container-name: theme;
}

/* the root element responds to user preference */
@media (prefers-color-scheme: dark) {
  html {
    --background-color: var(--bg-dark);
    color: white;
  }
}

/* in a theme container with a light background… */
@container theme style(--background-color: var(--bg-light)) {
  /* the footer switches to dark mode */
  footer {
    --background-color: var(--bg-dark);
    color: white;
  }

  /* links have a dark color */
  a:any-link {
    color: mediumvioletred;
  }
}

/* in a theme container with a dark background… */
@container theme style(--background-color: var(--bg-dark)) {
  /* the footer switches to light mode */
  footer {
    --background-color: var(--bg-light);
    color: black;
  }

  /* links have a light color */
  a:any-link {
    color: snow;
  }
}

@layer init {
  * {
    box-sizing: border-box;
  }
  html {
    height: 100%;
  }
  body {
    min-height: 100%;
    display: grid;
    grid-template-columns: minmax(min-content, min(100%, 65ch));
    place-content: center;
    padding: 1em;
  }

  footer {
    padding: 1em;
  }
}
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JS
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