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CSS

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HTML 

              
                <main lang=en>
  <!-- Updated March 2025 to animate in Chrome -->
  <h1>One details element open at a time &ndash; An accordion</h1>
  <p>Animated by CSS in that Chrome, others to follow.</p>
  
  <div class=flex>
  
    <div class=accordion>
      
      <!-- name attribute added 14/12/2023 for native accordian support in Safari 17.2, Chrome 120, Edge 120. And eventually Firefox -->

      <details name=accordian1>
        <summary>One</summary>
        <div aria-label=Yes>👍</div>
      </details>

      <details name=accordian1>
        <summary>Two</summary>
        <div aria-label="Yes, yes">👍👍</div>
      </details>

      <details name=accordian1>
        <summary>Three</summary>
        <div aria-label="Yes, yes, yes">👍👍👍</div>
      </details>

    </div>

    <div class=accordion lang=es>

      <details name=accordian2>
        <summary>Uno</summary>
        <div aria-label=Bueno>👌</div>
      </details>

      <details name=accordian2>
        <summary>Dos</summary>
        <div aria-label="Bueno, bueno">👌👌</div>
      </details>

      <details name=accordian2>
        <summary>Tres</summary>
        <div aria-label="Bueno, bueno, bueno">👌👌👌</div>
      </details>

    </div>

    <div class=accordion lang=fr>

      <details name=accordian3>
        <summary>Un</summary>
        <div aria-label="Tu gères">🤘</div>
      </details>

      <details name=accordian3>
        <summary>Deux</summary>
        <div aria-label="Tu gères, tu gères">🤘🤘</div>
      </details>

      <details name=accordian3>
        <summary>Trois</summary>
        <div aria-label="Tu gères, tu gères, tu gères">🤘🤘🤘</div>
      </details>

    </div>
    
  </div>
  
  <p>Also see: <a href="https://codepen.io/2kool2/pen/MWRLOrv?editors=1000" target="_self">Multi-level accordions</a></p>

</main>
!

CSS 

              
                /* CSS not required, but makes the page purtie */

body {
  background-color: #1a1a1a;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 2056 2056' xmlns='http://www.w3.org/2000/svg'%3E%3CradialGradient id='g73'%3E%3Cstop offset='0%' stop-color='%23222'/%3E%3Cstop offset='100%' stop-color='%23000'/%3E%3C/radialGradient%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.19'/%3E%3C/filter%3E%3Crect width='2056' height='2056' fill='url(%23g73)' opacity='1.25'/%3E%3Crect width='2056' height='2056' filter='url(%23noiseFilter)' opacity='0.25'/%3E%3C/svg%3E");
  background-position: center;
  color: #fff;
  display: grid;
  font-family: sans-serif;
  font-size: 1.25rem;
  font-weight: 100;
  margin: 0;
  min-height: 100vh;
  place-content: center;
  text-shadow: 0 2px 2px #000;
}
* {
  margin: 0;
}
* + * {
  margin-top: 1rem;
}
main {
  display: block;
  margin: 0 1rem;
  min-height: 14rem;
}
h1 {
  font-size: 1.5rem;
  font-weight: 100;
  margin-bottom: 0;
}
p {
  font-size: 1rem;
  margin: 2rem auto;
  text-align: center;
}
h1 + p {
  margin:1rem auto 2rem;
}
a, a:visited {
  color: #fff;
  text-underline-offset: .15em;
}

.flex {
  display: flex;
  gap: 1rem;
}
.flex > div {
  margin: 0;
  width: 33%;
  border: 1px solid #333;
  background-color: rgb(0,0,0,.0625);
  padding: 0.25rem .5rem;
}

summary:focus-visible {
  outline: 2px solid #007aff;
  outline-offset: 8px;
}


/* 

Coming soon to all browsers not just Chrome.
Animating a details summary dropdown with CSS in a progressive enhancement manner which doesn't require any JavaScript.

14/03/2025 - Doesn't animate in Firefox or Safari yet. Still opens & closes but without the animation (progressive enhancement).

Hopefully, Interop 2025 will address the browser differences when it comes to details & summary. (I'm hoping the a11y issues in iOS Safari will finally be resolved!)

*/

:root {
  interpolate-size: allow-keywords;
}
details::details-content {
  block-size: 0;
  overflow: hidden;
  transition:
    block-size .3s ease-in-out,
    content-visibility .3s ease-in-out;
  transition-behavior: allow-discrete;
}
details[open]::details-content {
  block-size: auto;
}
summary {
  line-height: 1.3;
  margin-inline-start: 1rem;
  /* Maintain indent over multiple lines */
  list-style-position: outside;
  cursor: pointer;
  position: relative;
}
!

JS 

              
                // As of 2025 JS is no longer needed as all modern browsers now support the name attribute on a details element.

// JS was only required to keep one element open at a time in older browsers. The fallback is to default details behaviour.


// Kept for archieval purposes:
/*
const accordions = (_ => {

  // Class used, but could be a data attribute or custom element
  const accordionQuery = '.accordion';

  const accordionClicked = event => {
    const summary = event.target;
    if (summary.tagName.toLowerCase() !== 'summary') return;

    const currentDetails = summary.parentElement;
    const accordion = currentDetails.closest(accordionQuery);

    const allOpenDetails = accordion.querySelectorAll('details[open]');
    for (const details of allOpenDetails) {

      // But not the clicked summary
      if (details === currentDetails) continue;

      details.removeAttribute('open');
    }
  };

  // Consider each group of details (individual accordian)
  const accordions = document.querySelectorAll(accordionQuery);
  for (const accordion of accordions) {
    accordion.addEventListener('click', accordionClicked);
  }

})();

// */
!
999px

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