Bootstrap Image Lightbox Gallery Modal — Free Snippet

<div class="container py-5">
  <div class="row g-2" id="bslightGrid">
    <div class="col-4"><div class="bslight-thumb" style="--h:230" data-idx="0"></div></div>
    <div class="col-4"><div class="bslight-thumb" style="--h:20" data-idx="1"></div></div>
    <div class="col-4"><div class="bslight-thumb" style="--h:150" data-idx="2"></div></div>
    <div class="col-4"><div class="bslight-thumb" style="--h:300" data-idx="3"></div></div>
    <div class="col-4"><div class="bslight-thumb" style="--h:60" data-idx="4"></div></div>
    <div class="col-4"><div class="bslight-thumb" style="--h:180" data-idx="5"></div></div>
  </div>
</div>

<div class="modal fade" id="bslightModal" tabindex="-1">
  <div class="modal-dialog modal-dialog-centered modal-lg">
    <div class="modal-content bslight-modal-content">
      <button type="button" class="btn-close btn-close-white position-absolute top-0 end-0 m-3" style="z-index:2" data-bs-dismiss="modal" aria-label="Close"></button>
      <div class="bslight-stage">
        <button class="bslight-nav bslight-prev" id="bslightPrev" aria-label="Previous image">‹</button>
        <div class="bslight-full" id="bslightFull"></div>
        <button class="bslight-nav bslight-next" id="bslightNext" aria-label="Next image">›</button>
      </div>
      <div class="text-center py-2 text-white-50 small" id="bslightCounter">1 / 6</div>
    </div>
  </div>
</div>

.bslight-thumb {
  aspect-ratio: 1; border-radius: 8px; cursor: pointer;
  background: linear-gradient(135deg, hsl(calc(var(--h)) 60% 75%), hsl(calc(var(--h) + 40) 60% 55%));
  transition: transform .15s;
}
.bslight-thumb:hover { transform: scale(0.97); }

.bslight-modal-content { background: #111827; border: none; }
.bslight-stage { position: relative; display: flex; align-items: center; }
.bslight-full { aspect-ratio: 16/9; width: 100%; background: linear-gradient(135deg, hsl(calc(var(--h,0)) 60% 60%), hsl(calc(var(--h,0) + 40) 60% 40%)); }
.bslight-nav {
  position: absolute; top: 50%; transform: translateY(-50%);
  width: 40px; height: 40px; border-radius: 50%; border: none;
  background: rgba(255,255,255,.15); color: #fff; font-size: 22px; cursor: pointer; z-index: 2;
}
.bslight-nav:hover { background: rgba(255,255,255,.3); }
.bslight-prev { left: 12px; }
.bslight-next { right: 12px; }

const HUES = [230, 20, 150, 300, 60, 180];
const modalEl = document.getElementById('bslightModal');
const modal = new bootstrap.Modal(modalEl);
const full = document.getElementById('bslightFull');
const counter = document.getElementById('bslightCounter');
let current = 0;

function render() {
  full.style.setProperty('--h', HUES[current]);
  counter.textContent = (current + 1) + ' / ' + HUES.length;
}

document.getElementById('bslightGrid').addEventListener('click', e => {
  const thumb = e.target.closest('.bslight-thumb');
  if (!thumb) return;
  current = Number(thumb.dataset.idx);
  render();
  modal.show();
});

document.getElementById('bslightPrev').addEventListener('click', () => {
  current = (current - 1 + HUES.length) % HUES.length;
  render();
});
document.getElementById('bslightNext').addEventListener('click', () => {
  current = (current + 1) % HUES.length;
  render();
});

// Arrow keys navigate while the lightbox is open — a standard gallery
// expectation Bootstrap's Modal doesn't provide on its own.
modalEl.addEventListener('keydown', e => {
  if (e.key === 'ArrowLeft') document.getElementById('bslightPrev').click();
  if (e.key === 'ArrowRight') document.getElementById('bslightNext').click();
});