Bootstrap 5 Expanding Image Gallery on Hover

<section class="wdw-stage">
  <div class="container" style="max-width: 1100px">
    <div class="text-center mb-4">
      <span class="wdw-eyebrow">Gallery</span>
      <h2 class="wdw-heading display-6 mt-1 mb-2">Five places worth the trip</h2>
      <p class="wdw-muted mb-0">Hover, tap or focus a panel to expand it.</p>
    </div>
    <div class="eg-gallery d-flex flex-column flex-md-row gap-2 gap-md-3" id="egGallery" role="group" aria-label="Image gallery">
    <button type="button" class="eg-panel btn border-0 p-0 position-relative overflow-hidden rounded-4" aria-pressed="false" style="--eg-img:url('https://images.unsplash.com/photo-1506744038136-46273834b3fb?auto=format&fit=crop&w=1000&q=70')">
      <span class="eg-label position-absolute bottom-0 start-0 end-0 p-3 d-flex flex-column text-start text-white"><span class="eg-num small fw-bold opacity-75">01</span><span class="eg-title fw-bold">Valley</span><span class="eg-sub small">Yosemite, USA</span></span>
    </button>
    <button type="button" class="eg-panel btn border-0 p-0 position-relative overflow-hidden rounded-4" aria-pressed="false" style="--eg-img:url('https://images.unsplash.com/photo-1469474968028-56623f02e42e?auto=format&fit=crop&w=1000&q=70')">
      <span class="eg-label position-absolute bottom-0 start-0 end-0 p-3 d-flex flex-column text-start text-white"><span class="eg-num small fw-bold opacity-75">02</span><span class="eg-title fw-bold">Ridge</span><span class="eg-sub small">Scottish Highlands</span></span>
    </button>
    <button type="button" class="eg-panel btn border-0 p-0 position-relative overflow-hidden rounded-4 is-active" aria-pressed="true" style="--eg-img:url('https://images.unsplash.com/photo-1441974231531-c6227db76b6e?auto=format&fit=crop&w=1000&q=70')">
      <span class="eg-label position-absolute bottom-0 start-0 end-0 p-3 d-flex flex-column text-start text-white"><span class="eg-num small fw-bold opacity-75">03</span><span class="eg-title fw-bold">Forest</span><span class="eg-sub small">Black Forest, DE</span></span>
    </button>
    <button type="button" class="eg-panel btn border-0 p-0 position-relative overflow-hidden rounded-4" aria-pressed="false" style="--eg-img:url('https://images.unsplash.com/photo-1501785888041-af3ef285b470?auto=format&fit=crop&w=1000&q=70')">
      <span class="eg-label position-absolute bottom-0 start-0 end-0 p-3 d-flex flex-column text-start text-white"><span class="eg-num small fw-bold opacity-75">04</span><span class="eg-title fw-bold">Lake</span><span class="eg-sub small">Dolomites, Italy</span></span>
    </button>
    <button type="button" class="eg-panel btn border-0 p-0 position-relative overflow-hidden rounded-4" aria-pressed="false" style="--eg-img:url('https://images.unsplash.com/photo-1470071459604-3b5ec3a7fe05?auto=format&fit=crop&w=1000&q=70')">
      <span class="eg-label position-absolute bottom-0 start-0 end-0 p-3 d-flex flex-column text-start text-white"><span class="eg-num small fw-bold opacity-75">05</span><span class="eg-title fw-bold">Hills</span><span class="eg-sub small">Faroe Islands</span></span>
    </button>
    </div>
  </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 */
.eg-gallery { height: 26rem; }
.eg-panel { flex: 1 1 0; min-width: 0; background-image: var(--eg-img); background-size: cover; background-position: center; transition: flex-grow .6s cubic-bezier(.2,.7,.2,1); box-shadow: var(--wdw-shadow-sm); }
.eg-panel::after { content: ""; position: absolute; inset: 0; background: linear-gradient(to top, rgba(15,17,40,.8), rgba(15,17,40,.05) 55%); }
.eg-panel:not(.is-active)::after { background: linear-gradient(to top, rgba(15,17,40,.75), rgba(15,17,40,.3)); }
.eg-panel.is-active { flex-grow: 4; }
.eg-panel:focus-visible { outline: 3px solid #fff; outline-offset: -6px; box-shadow: inset 0 0 0 7px rgba(15,17,40,.85), var(--wdw-shadow-sm); }
.eg-label { z-index: 1; }
.eg-num { letter-spacing: .1em; }
.eg-title { font-size: 1.35rem; white-space: nowrap; }
.eg-sub { color: rgba(255,255,255,.85); white-space: nowrap; max-height: 0; opacity: 0; transition: opacity .4s .15s, max-height .4s; }
.eg-panel.is-active .eg-sub { max-height: 2rem; opacity: 1; }
.eg-panel:not(.is-active) .eg-num { display: none; }
.eg-panel:not(.is-active) .eg-title { writing-mode: vertical-rl; transform: rotate(180deg); align-self: flex-start; font-size: 1.05rem; }
@media (max-width: 767.98px) {
  .eg-gallery { height: 34rem; }
  .eg-panel:not(.is-active) .eg-title { writing-mode: horizontal-tb; transform: none; font-size: 1rem; }
  .eg-panel.is-active { flex-grow: 5; }
}
@media (prefers-reduced-motion: reduce) { .eg-panel, .eg-sub { transition: none; } }

(function () {
  function initExpandingGallery() {
    var gallery = document.getElementById('egGallery');
    if (!gallery) return;
    var panels = gallery.querySelectorAll('.eg-panel');
    function activate(p) {
      if (p.classList.contains('is-active')) return;
      panels.forEach(function (x) {
        var on = x === p;
        x.classList.toggle('is-active', on);
        x.setAttribute('aria-pressed', on ? 'true' : 'false');
      });
    }
    panels.forEach(function (p) {
      ['mouseenter', 'focus', 'click'].forEach(function (ev) {
        p.addEventListener(ev, function () { activate(p); });
      });
    });
  }
  initExpandingGallery();
})();