CSS Grid Mask Poster Layout with Bootstrap 5

<section class="wdw-stage">
  <div class="container" style="max-width: 960px">
    <div class="text-center mb-3">
      <span class="wdw-eyebrow">CSS Grid</span>
      <h2 class="wdw-heading h3 mb-1">Grid as a mask</h2>
      <p class="wdw-muted mb-0">Solid cells cover a full-bleed photo. Cells left empty become windows.</p>
    </div>
    <figure class="gm-poster wdw-card mb-0">
      <div class="gm-photo" role="img" aria-label="Night mountain landscape with stars, visible through the poster windows"></div>
      <div class="gm-grid" id="gm-grid">
        <span class="gm-win gm-w1" aria-hidden="true"></span>
        <span class="gm-win gm-w2" aria-hidden="true"></span>
        <span class="gm-win gm-w3" aria-hidden="true"></span>
        <span class="gm-win gm-w4" aria-hidden="true"></span>
        <span class="gm-win gm-w5" aria-hidden="true"></span>
        <p class="gm-cap gm-cap1">An editorial poster built on an 8-column grid. Every tile is a plain element.</p>
        <p class="gm-name wdw-aurora"><span>Ada</span>Rivers</p>
        <p class="gm-cap gm-cap2">Remove a cell's background and the photo shows through.</p>
      </div>
    </figure>
  </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 */
.gm-poster { position: relative; overflow: hidden; container-type: inline-size; aspect-ratio: 2 / 1; background: #1e1b4b; }
.gm-photo { position: absolute; inset: 0; background: url("https://images.unsplash.com/photo-1519681393784-d120267933ba?auto=format&fit=crop&w=1600&q=70") center / cover; }
.gm-grid { position: absolute; inset: 0; display: grid; grid-template-columns: repeat(8, 1fr); grid-template-rows: repeat(6, 1fr); grid-auto-rows: 0; overflow: hidden; }
.gm-grid > i { background: #1e1b4b; }
.gm-win { background: none; }
.gm-w1 { grid-area: 1 / 2 / 3 / 5; }
.gm-w2 { grid-area: 5 / 1 / 7 / 3; }
.gm-w3 { grid-area: 2 / 6 / 4 / 9; }
.gm-w4 { grid-area: 4 / 5 / 6 / 7; }
.gm-w5 { grid-area: 5 / 7 / 7 / 9; }
.gm-cap { z-index: 1; background: #1e1b4b; margin: 0; padding: .5rem 1rem; color: rgba(255,255,255,.88); font-size: clamp(.8rem, 1.5cqw, 1rem); line-height: 1.45; display: flex; align-items: center; }
.gm-cap1 { grid-area: 1 / 5 / 2 / 9; }
.gm-cap2 { grid-area: 6 / 3 / 7 / 6; }
.gm-name { z-index: 1; grid-area: 3 / 1 / 5 / 5; margin: 0; display: flex; flex-direction: column; align-items: flex-start; justify-content: center; color: #fff; font-weight: 800; letter-spacing: -.04em; line-height: .95; font-size: 11cqw; padding-inline: 1.25rem; }
.gm-name span { font-weight: 600; font-size: .3em; letter-spacing: .16em; text-transform: uppercase; color: #c7d2fe; margin-bottom: .3em; }
@media (max-width: 575.98px) {
  .gm-poster { aspect-ratio: 5 / 8; }
  .gm-grid { grid-template-columns: repeat(4, 1fr); grid-template-rows: repeat(8, 1fr); }
  .gm-w1 { grid-area: 1 / 1 / 3 / 3; }
  .gm-w5 { grid-area: 1 / 4 / 3 / 5; }
  .gm-name { grid-area: 3 / 1 / 4 / 5; font-size: 17cqw; flex-direction: row; align-items: baseline; gap: .2em; }
  .gm-name span { font-size: .3em; }
  .gm-w4 { grid-area: 4 / 1 / 6 / 2; }
  .gm-w2 { grid-area: 4 / 2 / 6 / 5; }
  .gm-cap1 { grid-area: 6 / 1 / 7 / 5; font-size: .85rem; }
  .gm-w3 { grid-area: 7 / 1 / 8 / 5; }
  .gm-cap2 { grid-area: 8 / 1 / 9 / 5; font-size: .85rem; }
}

function initGridMask() {
  var grid = document.getElementById('gm-grid');
  if (!grid) return;
  var frag = document.createDocumentFragment();
  for (var i = 0; i < 48; i++) {
    var tile = document.createElement('i');
    tile.setAttribute('aria-hidden', 'true');
    frag.appendChild(tile);
  }
  grid.appendChild(frag);
}
initGridMask();