Bootstrap 5 Expanding Image Accordion Gallery

<section class="wdw-stage">
  <div class="container" style="max-width: 1040px">
    <div class="text-center mb-4">
      <span class="wdw-eyebrow">Gallery</span>
      <h1 class="h2 wdw-heading mt-1 mb-0">Meet the neighbourhood cats</h1>
    </div>
    <ul class="zoom-accordion list-unstyled m-0" aria-label="Cat gallery">
      <li class="zoom-panel is-active">
        <button type="button" class="zoom-btn" aria-expanded="true">
          <img src="https://images.unsplash.com/photo-1514888286974-6c03e2ca1dba?auto=format&fit=crop&w=900&q=70" alt="Plotting Cat" loading="lazy">
          <span class="zoom-caption"><strong>Plotting Cat</strong><small>Always up to something.</small></span>
        </button>
      </li>
      <li class="zoom-panel">
        <button type="button" class="zoom-btn" aria-expanded="false">
          <img src="https://images.unsplash.com/photo-1543852786-1cf6624b9987?auto=format&fit=crop&w=900&q=70" alt="Curious Cat" loading="lazy">
          <span class="zoom-caption"><strong>Curious Cat</strong><small>Needs to inspect everything.</small></span>
        </button>
      </li>
      <li class="zoom-panel">
        <button type="button" class="zoom-btn" aria-expanded="false">
          <img src="https://images.unsplash.com/photo-1592194996308-7b43878e84a6?auto=format&fit=crop&w=900&q=70" alt="Sleepy Cat" loading="lazy">
          <span class="zoom-caption"><strong>Sleepy Cat</strong><small>Naps are non-negotiable.</small></span>
        </button>
      </li>
      <li class="zoom-panel">
        <button type="button" class="zoom-btn" aria-expanded="false">
          <img src="https://images.unsplash.com/photo-1513245543132-31f507417b26?auto=format&fit=crop&w=900&q=70" alt="Prowling Cat" loading="lazy">
          <span class="zoom-caption"><strong>Prowling Cat</strong><small>Silent, patient, precise.</small></span>
        </button>
      </li>
      <li class="zoom-panel">
        <button type="button" class="zoom-btn" aria-expanded="false">
          <img src="https://images.unsplash.com/photo-1529778873920-4da4926a72c2?auto=format&fit=crop&w=900&q=70" alt="Cosy Cat" loading="lazy">
          <span class="zoom-caption"><strong>Cosy Cat</strong><small>Found the warmest spot.</small></span>
        </button>
      </li>
    </ul>
  </div>
</section>

/* Web Designer Wall library style — shared base for every Bootstrap 5 snippet.
   Indigo accent, Plus Jakarta Sans, soft cards, pill buttons. Works in light and dark. */
@import url("https://fonts.googleapis.com/css2?family=Plus+Jakarta+Sans:wght@400;500;600;700;800&display=swap");

:root,
[data-bs-theme="light"] {
  --wdw-font: "Plus Jakarta Sans", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --bs-body-font-family: var(--wdw-font);
  --bs-primary: #4f46e5;
  --bs-primary-rgb: 79, 70, 229;
  --bs-primary-text-emphasis: #3730a3;
  --bs-primary-bg-subtle: #eef2ff;
  --bs-primary-border-subtle: #c7d2fe;
  --bs-link-color: #4f46e5;
  --bs-link-color-rgb: 79, 70, 229;
  --bs-link-hover-color: #4338ca;
  --bs-link-hover-color-rgb: 67, 56, 202;
  --bs-focus-ring-color: rgba(79, 70, 229, 0.25);
  --bs-border-radius: 0.75rem;
  --bs-border-radius-lg: 1rem;
  --bs-border-radius-xl: 1.25rem;
  --wdw-radius-card: 1.25rem;
  --wdw-shadow: 0 1px 2px rgba(16, 24, 40, 0.05), 0 16px 40px -16px rgba(16, 24, 40, 0.22);
  --wdw-shadow-sm: 0 1px 2px rgba(16, 24, 40, 0.06), 0 4px 12px -4px rgba(16, 24, 40, 0.12);
  --wdw-stage: #f5f6fb;
}

[data-bs-theme="dark"] {
  --bs-primary: #818cf8;
  --bs-primary-rgb: 129, 140, 248;
  --bs-primary-text-emphasis: #c7d2fe;
  --bs-primary-bg-subtle: rgba(129, 140, 248, 0.14);
  --bs-primary-border-subtle: rgba(129, 140, 248, 0.35);
  --bs-link-color: #a5b4fc;
  --bs-link-color-rgb: 165, 180, 252;
  --bs-link-hover-color: #c7d2fe;
  --bs-link-hover-color-rgb: 199, 210, 254;
  --bs-focus-ring-color: rgba(129, 140, 248, 0.35);
  --wdw-shadow: 0 1px 2px rgba(0, 0, 0, 0.4), 0 16px 40px -16px rgba(0, 0, 0, 0.7);
  --wdw-shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4), 0 4px 12px -4px rgba(0, 0, 0, 0.5);
  --wdw-stage: #0f1117;
}

body { font-family: var(--wdw-font); -webkit-font-smoothing: antialiased; }

/* Bootstrap compiles its blue into these components; point them at the accent. */
.btn-primary {
  --bs-btn-bg: var(--bs-primary); --bs-btn-border-color: var(--bs-primary);
  --bs-btn-hover-bg: #4338ca; --bs-btn-hover-border-color: #4338ca;
  --bs-btn-active-bg: #3730a3; --bs-btn-active-border-color: #3730a3;
  --bs-btn-disabled-bg: var(--bs-primary); --bs-btn-disabled-border-color: var(--bs-primary);
  --bs-btn-focus-shadow-rgb: var(--bs-primary-rgb);
}
[data-bs-theme="dark"] .btn-primary { --bs-btn-color: #0f1117; --bs-btn-hover-bg: #a5b4fc; --bs-btn-hover-border-color: #a5b4fc; --bs-btn-hover-color: #0f1117; --bs-btn-active-color: #0f1117; }
.btn-outline-primary {
  --bs-btn-color: var(--bs-primary); --bs-btn-border-color: var(--bs-primary);
  --bs-btn-hover-bg: var(--bs-primary); --bs-btn-hover-border-color: var(--bs-primary);
  --bs-btn-active-bg: var(--bs-primary); --bs-btn-active-border-color: var(--bs-primary);
  --bs-btn-focus-shadow-rgb: var(--bs-primary-rgb);
}
.btn { --bs-btn-font-weight: 600; min-height: 44px; display: inline-flex; align-items: center; justify-content: center; gap: .5rem; }
.btn-sm { min-height: 36px; }
.form-control, .form-select { min-height: 44px; border-radius: .75rem; }
.form-control:focus, .form-select:focus, .form-check-input:focus { border-color: rgba(var(--bs-primary-rgb), .6); box-shadow: 0 0 0 .25rem var(--bs-focus-ring-color); }
.form-check-input:checked { background-color: var(--bs-primary); border-color: var(--bs-primary); }
.nav-pills { --bs-nav-pills-link-active-bg: var(--bs-primary); }
.nav { --bs-nav-link-color: var(--bs-secondary-color); --bs-nav-link-hover-color: var(--bs-emphasis-color); }
.pagination { --bs-pagination-active-bg: var(--bs-primary); --bs-pagination-active-border-color: var(--bs-primary); --bs-pagination-color: var(--bs-body-color); --bs-pagination-focus-box-shadow: 0 0 0 .25rem var(--bs-focus-ring-color); }
.progress, .progress-stacked { --bs-progress-bar-bg: var(--bs-primary); }
.list-group { --bs-list-group-active-bg: var(--bs-primary); --bs-list-group-active-border-color: var(--bs-primary); }
.dropdown-menu { --bs-dropdown-link-active-bg: var(--bs-primary); border-radius: .875rem; box-shadow: var(--wdw-shadow-sm); }
.accordion { --bs-accordion-active-bg: var(--bs-primary-bg-subtle); --bs-accordion-active-color: var(--bs-primary-text-emphasis); --bs-accordion-btn-focus-box-shadow: 0 0 0 .25rem var(--bs-focus-ring-color); }
.badge { font-weight: 600; }

/* Library building blocks — use these instead of re-inventing them per snippet. */
.wdw-stage { min-height: 100vh; display: flex; align-items: center; background: var(--wdw-stage); padding-block: 3rem; }
.wdw-card { background: var(--bs-body-bg); border: 1px solid var(--bs-border-color-translucent); border-radius: var(--wdw-radius-card); box-shadow: var(--wdw-shadow); }
.wdw-card-sm { background: var(--bs-body-bg); border: 1px solid var(--bs-border-color-translucent); border-radius: 1rem; box-shadow: var(--wdw-shadow-sm); }
.wdw-aurora { position: relative; color: #fff; background: radial-gradient(60% 55% at 100% 0, #818cf8 0, transparent 70%), radial-gradient(65% 60% at 0 100%, #ec4899 0, transparent 65%), #1e1b4b; }
.wdw-eyebrow { display: inline-block; font-size: .75rem; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; color: var(--bs-primary); }
.wdw-heading { font-weight: 800; letter-spacing: -.02em; color: var(--bs-emphasis-color); }
.wdw-muted { color: var(--bs-secondary-color); }
.wdw-icon { width: 2.75rem; height: 2.75rem; flex: none; display: inline-flex; align-items: center; justify-content: center; border-radius: .875rem; background: var(--bs-primary-bg-subtle); color: var(--bs-primary); }

/* Component */
.zoom-accordion { display: flex; gap: .75rem; height: 30rem; }
.zoom-panel { flex: 1 1 0; min-width: 0; min-height: 0; transition: flex-grow .6s cubic-bezier(.2,.8,.2,1); }
.zoom-panel.is-active { flex-grow: 4.5; }
.zoom-btn { position: relative; display: block; width: 100%; height: 100%; padding: 0; border: 0; border-radius: 1.25rem; overflow: hidden; background: var(--bs-tertiary-bg); box-shadow: var(--wdw-shadow-sm); cursor: pointer; text-align: left; }
.zoom-btn:focus-visible { outline: 3px solid var(--bs-primary); outline-offset: 3px; }
.zoom-btn img { position: absolute; inset: 0; width: 100%; height: 100%; object-fit: cover; filter: brightness(.9) saturate(.7); transform: scale(1.12); transition: filter .6s, transform .8s cubic-bezier(.2,.8,.2,1); }
.zoom-panel.is-active img, .zoom-btn:hover img { filter: none; transform: scale(1); }
.zoom-btn::after { content: ""; position: absolute; inset: 0; opacity: 0; transition: opacity .5s; background: linear-gradient(to top, rgba(10,10,30,.85), transparent 60%); }
.zoom-panel.is-active .zoom-btn::after { opacity: 1; }
.zoom-caption { opacity: 0; transition: opacity .3s; position: absolute; z-index: 1; left: 1.1rem; right: 1.1rem; bottom: 1rem; color: #fff; display: flex; flex-direction: column; white-space: nowrap; overflow: hidden; }
.zoom-panel.is-active .zoom-caption { opacity: 1; transition-delay: .2s; }
.zoom-caption strong { font-size: 1.05rem; }
.zoom-caption small { opacity: 0; max-height: 0; color: rgba(255,255,255,.8); transition: opacity .4s .15s, max-height .4s; }
.zoom-panel.is-active .zoom-caption small { opacity: 1; max-height: 1.5rem; }
@media (max-width: 767.98px) {
  .zoom-accordion { flex-direction: column; height: 30rem; gap: .5rem; }
  .zoom-panel.is-active { flex-grow: 6; }
}
@media (prefers-reduced-motion: reduce) { .zoom-panel, .zoom-btn img { transition: none; } }

function initZoomAccordion() {
  const panels = document.querySelectorAll('.zoom-panel');
  if (!panels.length) return;
  let timer;
  const activate = (panel) => {
    panels.forEach((p) => {
      const on = p === panel;
      p.classList.toggle('is-active', on);
      p.querySelector('.zoom-btn').setAttribute('aria-expanded', on);
    });
  };
  panels.forEach((panel) => {
    const btn = panel.querySelector('.zoom-btn');
    btn.addEventListener('click', () => activate(panel));
    btn.addEventListener('focus', () => activate(panel));
    btn.addEventListener('mouseenter', () => {
      if (!matchMedia('(hover: hover)').matches) return;
      clearTimeout(timer);
      timer = setTimeout(() => activate(panel), 120);
    });
    btn.addEventListener('mouseleave', () => clearTimeout(timer));
  });
}
initZoomAccordion();