Accordion item icon

[scottdorman]

In Bootstrap 5, the chevron icon was added via a ::after pseudo-element, so we didn't have to manually include it in every accordion item's header.

<div class="accordion" id="accordionExample">
  <div class="accordion-item">
    <h2 class="accordion-header">
      <button class="accordion-button" type="button" data-bs-toggle="collapse" data-bs-target="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
        Accordion Item #1
      </button>
    </h2>
    <div id="collapseOne" class="accordion-collapse collapse show" data-bs-parent="#accordionExample">
      <div class="accordion-body"></div>
    </div>
  </div>
  <div class="accordion-item">
    <h2 class="accordion-header">
      <button class="accordion-button collapsed" type="button" data-bs-toggle="collapse" data-bs-target="#collapseTwo" aria-expanded="false" aria-controls="collapseTwo">
        Accordion Item #2
      </button>
    </h2>
    <div id="collapseTwo" class="accordion-collapse collapse" data-bs-parent="#accordionExample">
      <div class="accordion-body">
      </div>
    </div>
  </div>
</div>

Bootstrap 6 seems to have dropped this, which forces everyone to include the icon.

<details class="accordion-item" name="parentAccordion">
    <summary class="accordion-header">
         Choose options.
        <svg class="accordion-icon" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round"><path d="m2 5 6 6 6-6" /></svg>
    </summary>
    <div class="accordion-body"></div>
</details>

I get that this allows much greater, easier icon customization, but we could also use a CSS variable to store the SVG and override it with a custom style rule if we wanted.

Were there other reasons for this decision, and is there a way to revert to automatically including it? Even if we took a "hybrid" approach and included an accordion-icon element for placement and a CSS ::after rule, that seems less human-error-prone than having to remember to include it on every accordion header

[DahanItamar]

On the "why": the change came with #41953, which rebuilt the accordion on native <details>/<summary> with the name attribute. The PR description doesn't give a specific reason for moving the chevron into markup, so only the maintainers can answer that. Since v6 is still in alpha, this thread is the right place to push for an automatic icon.

You can get one back today, though, without touching the markup. In 6.0.0-alpha.1, the chevron's size, rotation and transition are all driven by accordion CSS variables. A ::after on .accordion-header can use the same variables, with the SVG stored in a custom property as you suggested:

.accordion {
  --accordion-auto-icon: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' fill='none' stroke='%23000' stroke-linecap='round' stroke-linejoin='round'%3e%3cpath d='m2 5 6 6 6-6'/%3e%3c/svg%3e");
}

.accordion-header:not(:has(.accordion-icon))::after {
  flex-shrink: 0;
  inline-size: var(--bs-accordion-btn-icon-width);
  block-size: var(--bs-accordion-btn-icon-width);
  margin-inline-start: auto;
  content: "";
  background-color: currentcolor;
  mask: var(--accordion-auto-icon) center / contain no-repeat;
  transition: var(--bs-accordion-btn-icon-transition);
}

.accordion-item[open] > .accordion-header:not(:has(.accordion-icon))::after {
  transform: var(--bs-accordion-btn-icon-transform);
}

@media (prefers-reduced-motion: reduce) {
  .accordion-header:not(:has(.accordion-icon))::after {
    transition: none;
  }
}

• mask + background-color: currentcolor gives the icon the header's text colour, including the open state and dark mode, like the inline SVG's stroke="currentColor". The SVG's own colour doesn't matter.
• :not(:has(.accordion-icon)) skips headers that already contain an icon, so you can mix both styles or move over gradually.
• To customise it, override --accordion-auto-icon on one accordion or globally.
• The .accordion-header is already display: flex, so margin-inline-start: auto puts the icon at the end, the same as .accordion-icon.

I tested it against the published bootstrap@6.0.0-alpha.1 CSS in headless Chrome. A header with no icon markup gets a 16px chevron, rotated -180deg when its item is open. Opening another item in the same name group rotates the new one and resets the old one. A header with an explicit .accordion-icon gets no ::after, so there's no duplicate. Visually it matches the explicit SVG.