Bootstrap 5 Expanding Column Menu

<section class="wdw-stage">
  <div class="container" style="max-width: 1040px">
    <div class="text-center mb-4">
      <span class="wdw-eyebrow">Navigation</span>
      <h2 class="wdw-heading h3 mb-1">Expanding column menu</h2>
      <p class="wdw-muted mb-0">Click, tap or focus a column to open it.</p>
    </div>
    <nav class="ec-strips wdw-card" aria-label="Sections">
      <div class="ec-strip wdw-aurora is-open">
        <button type="button" class="ec-btn" aria-expanded="true" aria-controls="ec-p1"><span class="ec-num">01</span><span class="ec-name">Overview</span></button>
        <div class="ec-panel" id="ec-p1"><p>A quick tour of everything we do, from first sketch to launch day.</p><a href="#" class="btn btn-light rounded-pill px-4">Open overview</a></div>
      </div>
      <div class="ec-strip bg-primary-subtle text-primary-emphasis">
        <button type="button" class="ec-btn" aria-expanded="false" aria-controls="ec-p2"><span class="ec-num">02</span><span class="ec-name">Work</span></button>
        <div class="ec-panel" id="ec-p2"><p>Selected projects across brand, product and web.</p><a href="#" class="btn btn-light rounded-pill px-4">See our work</a></div>
      </div>
      <div class="ec-strip bg-primary-subtle text-primary-emphasis">
        <button type="button" class="ec-btn" aria-expanded="false" aria-controls="ec-p3"><span class="ec-num">03</span><span class="ec-name">Studio</span></button>
        <div class="ec-panel" id="ec-p3"><p>Meet the small team behind the pixels.</p><a href="#" class="btn btn-light rounded-pill px-4">Meet the team</a></div>
      </div>
      <div class="ec-strip bg-primary-subtle text-primary-emphasis">
        <button type="button" class="ec-btn" aria-expanded="false" aria-controls="ec-p4"><span class="ec-num">04</span><span class="ec-name">Journal</span></button>
        <div class="ec-panel" id="ec-p4"><p>Notes on design, code and running a studio.</p><a href="#" class="btn btn-light rounded-pill px-4">Read the journal</a></div>
      </div>
      <div class="ec-strip bg-primary-subtle text-primary-emphasis">
        <button type="button" class="ec-btn" aria-expanded="false" aria-controls="ec-p5"><span class="ec-num">05</span><span class="ec-name">Contact</span></button>
        <div class="ec-panel" id="ec-p5"><p>Have a project in mind? Let's talk this week.</p><a href="#" class="btn btn-light rounded-pill px-4">Say hello</a></div>
      </div>
    </nav>
  </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 */
.ec-strips { display: flex; height: 440px; overflow: hidden; }
.ec-strip { flex: 1 1 0; min-width: 0; display: flex; flex-direction: column; justify-content: flex-end; padding: 1.5rem 1rem; border-inline-start: 1px solid var(--bs-border-color-translucent); transition: flex-grow .6s cubic-bezier(.23, 1, .32, 1); overflow: hidden; }
.ec-strip:first-child { border-inline-start: 0; }
.ec-strip.is-open { flex-grow: 4; padding: 2rem; }
.ec-btn { display: flex; flex-direction: column; align-items: flex-start; gap: .35rem; width: 100%; padding: 0; border: 0; background: none; color: inherit; text-align: start; border-radius: .5rem; margin-bottom: auto; min-height: 44px; }
.ec-btn:focus-visible { outline: 3px solid var(--bs-primary); outline-offset: 4px; }
.is-open .ec-btn:focus-visible { outline-color: #fff; }
.ec-num { font-size: .85rem; font-weight: 700; letter-spacing: .12em; }
.is-open .ec-num { color: rgba(255,255,255,.92); }
.ec-name { font-size: 1.05rem; font-weight: 700; letter-spacing: -.01em; overflow-wrap: anywhere; }
.is-open .ec-name { font-size: clamp(1.75rem, 3.4vw, 2.75rem); font-weight: 800; letter-spacing: -.03em; line-height: 1.05; margin-top: auto; }
.ec-panel { max-height: 0; opacity: 0; visibility: hidden; transform: translateY(12px); transition: opacity .3s ease, transform .3s ease, max-height .4s ease, visibility 0s .4s; }
.ec-panel p { margin: .75rem 0 1.25rem; font-size: 1.1rem; line-height: 1.5; color: rgba(255,255,255,.92); max-width: 28rem; }
.ec-panel .btn-light:focus-visible { outline: 3px solid #fff; outline-offset: 3px; }
.ec-strip.is-open .ec-panel { max-height: 12rem; opacity: 1; transform: none; visibility: visible; transition: opacity .35s ease .2s, transform .35s ease .2s, max-height .4s ease, visibility 0s; }
@media (max-width: 767.98px) {
  .ec-strips { flex-direction: column; height: 540px; }
  .ec-strip { flex-direction: column; justify-content: center; padding: .5rem 1.25rem; border-inline-start: 0; border-top: 1px solid var(--bs-border-color-translucent); }
  .ec-strip:first-child { border-top: 0; }
  .ec-strip.is-open { flex-grow: 4; padding: 1.25rem; justify-content: flex-end; }
  .ec-btn { flex-direction: row; align-items: baseline; gap: 1rem; margin-bottom: 0; }
  .is-open .ec-btn { flex-direction: column; gap: .35rem; }
  .is-open .ec-name { font-size: 2rem; }
}
@media (prefers-reduced-motion: reduce) { .ec-strip, .ec-panel { transition: none !important; } }
.is-open .ec-btn { margin-top: auto; margin-bottom: 0; }
.is-open .ec-name { margin-top: 0; }

function initExpandingColumns() {
  var strips = document.querySelectorAll('.ec-strip');
  if (!strips.length) return;
  var canHover = window.matchMedia('(hover: hover) and (min-width: 768px)');
  var timer = null;
  function open(target) {
    strips.forEach(function (s) {
      var on = s === target;
      s.classList.toggle('is-open', on);
      s.classList.toggle('wdw-aurora', on);
      s.classList.toggle('bg-primary-subtle', !on);
      s.classList.toggle('text-primary-emphasis', !on);
      s.querySelector('.ec-btn').setAttribute('aria-expanded', on);
    });
  }
  strips.forEach(function (s) {
    var btn = s.querySelector('.ec-btn');
    btn.addEventListener('click', function () { open(s); });
    btn.addEventListener('focus', function () { open(s); });
    s.addEventListener('mouseenter', function () {
      if (!canHover.matches) return;
      clearTimeout(timer);
      timer = setTimeout(function () { open(s); }, 180);
    });
    s.addEventListener('mouseleave', function () { clearTimeout(timer); });
  });
}
initExpandingColumns();