Bootstrap 5 Signup Form with Flip Animation

<section class="wdw-stage">
  <div class="container" style="max-width:920px">
    <div class="flip" id="signupFlip">
      <div class="flip-inner">
        <div class="flip-face wdw-card overflow-hidden" id="faceFront">
          <div class="row g-0 h-100">
            <div class="col-md-5 wdw-aurora p-4 p-lg-5 d-flex flex-column justify-content-between">
              <span class="fw-bold fs-5"><i class="bi bi-stars"></i> Lumen</span>
              <div class="py-4">
                <h2 class="fw-bold mb-3 su-brand-title">Start building something great</h2>
                <ul class="list-unstyled mb-0 su-points">
                  <li><i class="bi bi-check-circle-fill"></i> Free for 14 days</li>
                  <li><i class="bi bi-check-circle-fill"></i> No credit card required</li>
                  <li><i class="bi bi-check-circle-fill"></i> Cancel any time</li>
                </ul>
              </div>
            </div>
            <form class="col-md-7 p-4 p-lg-5" id="signupForm" novalidate>
              <h1 class="h3 wdw-heading mb-1">Create your account</h1>
              <p class="wdw-muted mb-4">Already have one? <a href="#" class="fw-semibold">Log in</a></p>
              <div class="form-floating mb-3">
                <input type="text" class="form-control" id="suName" placeholder="Full name" autocomplete="name" required>
                <label for="suName">Full name</label>
              </div>
              <div class="form-floating mb-3">
                <input type="email" class="form-control" id="suEmail" placeholder="Email address" autocomplete="email" required>
                <label for="suEmail">Email address</label>
                <div class="invalid-feedback">Enter a valid email address.</div>
              </div>
              <div class="input-group mb-3">
                <div class="form-floating flex-grow-1">
                  <input type="password" class="form-control" id="suPass" placeholder="Password" autocomplete="new-password" minlength="8" required>
                  <label for="suPass">Password (8+ characters)</label>
                </div>
                <button class="btn btn-outline-secondary" type="button" id="suToggle" aria-label="Show password" aria-pressed="false" style="min-width:48px"><i class="bi bi-eye"></i></button>
              </div>
              <div class="form-check mb-4">
                <input class="form-check-input" type="checkbox" id="suTerms" required>
                <label class="form-check-label small" for="suTerms">I agree with the <a href="#">Terms & Conditions</a></label>
              </div>
              <button type="submit" class="btn btn-primary rounded-pill w-100 btn-lg">Sign up</button>
              <p class="small text-danger mt-3 mb-0" id="suError" role="alert" hidden></p>
            </form>
          </div>
        </div>
        <div class="flip-face flip-back wdw-card d-flex align-items-center justify-content-center text-center p-4 p-lg-5" id="faceBack" aria-hidden="true">
          <div>
            <span class="wdw-icon mx-auto mb-4" style="width:4rem;height:4rem;font-size:1.75rem"><i class="bi bi-check-lg"></i></span>
            <h2 class="wdw-heading mb-2">Welcome aboard, <span id="suWho">friend</span></h2>
            <p class="wdw-muted mb-4">We sent a confirmation link to <strong id="suMail" class="text-body"></strong>.</p>
            <button type="button" class="btn btn-outline-primary rounded-pill px-4" id="suBack">Back to sign up</button>
          </div>
        </div>
      </div>
    </div>
  </div>
</section>

@import url("https://cdnjs.cloudflare.com/ajax/libs/bootstrap-icons/1.11.3/font/bootstrap-icons.min.css");
/* 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 */
.flip { perspective: 1600px; }
.flip-inner { display: grid; transition: transform .8s cubic-bezier(.4,.2,.2,1); transform-style: preserve-3d; }
.flip.flipped .flip-inner { transform: rotateY(180deg); }
.flip-face { grid-area: 1 / 1; backface-visibility: hidden; -webkit-backface-visibility: hidden; }
.flip-back { transform: rotateY(180deg); }
.su-brand-title { font-size: clamp(1.4rem, 3vw, 1.9rem); letter-spacing: -.02em; line-height: 1.2; }
.su-points li { display: flex; gap: .6rem; align-items: center; padding: .3rem 0; color: rgba(255,255,255,.88); }
.su-points i { color: #a5b4fc; }
.input-group > .btn-outline-secondary { --bs-btn-color: var(--bs-secondary-color); --bs-btn-border-color: var(--bs-border-color); --bs-btn-hover-bg: var(--bs-tertiary-bg); --bs-btn-hover-color: var(--bs-emphasis-color); --bs-btn-hover-border-color: var(--bs-border-color); border-radius: 0 .75rem .75rem 0; }
.input-group > .form-floating > .form-control { border-radius: .75rem 0 0 .75rem; }
.form-floating > .form-control { min-height: calc(3.5rem + 2px); }
@media (prefers-reduced-motion: reduce) { .flip-inner { transition: none; } }

function initSignupFlip() {
  const flip = document.getElementById('signupFlip');
  const form = document.getElementById('signupForm');
  if (!flip || !form) return;
  const front = document.getElementById('faceFront'), back = document.getElementById('faceBack');
  const err = document.getElementById('suError');
  const setFace = (showBack) => {
    flip.classList.toggle('flipped', showBack);
    front.setAttribute('aria-hidden', showBack);
    back.setAttribute('aria-hidden', !showBack);
    front.inert = showBack;
    back.inert = !showBack;
  };
  back.inert = true;

  const pass = document.getElementById('suPass'), toggle = document.getElementById('suToggle');
  toggle.addEventListener('click', () => {
    const show = pass.type === 'password';
    pass.type = show ? 'text' : 'password';
    toggle.setAttribute('aria-pressed', show);
    toggle.setAttribute('aria-label', show ? 'Hide password' : 'Show password');
    toggle.firstElementChild.className = show ? 'bi bi-eye-slash' : 'bi bi-eye';
  });

  form.addEventListener('submit', (e) => {
    e.preventDefault();
    const name = form.suName.value.trim(), email = form.suEmail;
    let msg = '';
    if (!name) msg = 'Please enter your name.';
    else if (!email.checkValidity() || !email.value) msg = 'Please enter a valid email address.';
    else if (pass.value.length < 8) msg = 'Password must be at least 8 characters.';
    else if (!form.suTerms.checked) msg = 'Please accept the terms to continue.';
    err.hidden = !msg;
    err.textContent = msg;
    if (msg) return;
    document.getElementById('suWho').textContent = name.split(' ')[0];
    document.getElementById('suMail').textContent = email.value;
    setFace(true);
    document.getElementById('suBack').focus({ preventScroll: true });
  });
  document.getElementById('suBack').addEventListener('click', () => { form.reset(); setFace(false); });
}
initSignupFlip();