Bootstrap 5 Login Modal for Vanilla JS

<!-- Requires Bootstrap 5.3 CSS + theme.css:
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/css/bootstrap.min.css">
<link rel="stylesheet" href="theme.css"> -->
<div>
  <button type="button" class="btn btn-brand fw-semibold rounded-2" data-open="open">Sign in</button>
  <div data-show="open">
    <div class="position-fixed top-0 start-0 w-100 h-100 z-3 d-flex align-items-center justify-content-center p-3 overlay" role="dialog" aria-modal="true" aria-labelledby="login-title">
      <div class="position-relative w-100 mw-md p-5 bg-body border shadow-sm rounded-3">
        <button type="button" class="position-absolute top-0 end-0 m-2 btn btn-sm btn-link link-secondary text-decoration-none" aria-label="Close" data-close="open">&times;</button>
        <h2 id="login-title" class="fs-4 fw-bold mb-1 text-body-emphasis">Welcome back</h2>
        <p class="small mb-4 text-body-secondary">Sign in to continue to your dashboard.</p>
        <form class="d-flex flex-column gap-3">
          <div>
            <label for="login-email" class="form-label small fw-medium">Email</label>
            <input id="login-email" type="email" autocomplete="email" placeholder="you@company.com" class="form-control rounded-2" required>
          </div>
          <div>
            <div class="d-flex align-items-center justify-content-between">
              <label for="login-password" class="form-label small fw-medium">Password</label>
              <a href="#" class="small text-brand fw-medium text-decoration-none">Forgot?</a>
            </div>
            <input id="login-password" type="password" autocomplete="current-password" placeholder="••••••••" class="form-control rounded-2" required>
          </div>
          <label class="d-flex align-items-center gap-2 small text-body">
            <input type="checkbox" class="form-check-input mt-0"> Remember me for 30 days
          </label>
          <button type="submit" class="btn btn-brand fw-semibold rounded-2 w-100">Sign in</button>
        </form>
        <div class="d-flex align-items-center gap-2 my-4">
          <span class="flex-fill border-top"></span>
          <span class="small text-uppercase text-body-secondary">or</span>
          <span class="flex-fill border-top"></span>
        </div>
        <button type="button" class="btn btn-outline-secondary fw-semibold rounded-2 w-100">Continue with Google</button>
        <p class="mt-4 text-center small text-body-secondary">No account? <a href="#" class="text-brand fw-medium text-decoration-none">Create one</a></p>
      </div>
    </div>
  </div>
</div>

<script>
  (() => {
    const state = { open: true };
    const actions = {  };
    const pair = (s) => s.split(':');
    const sync = () => {
      document.querySelectorAll('[data-show]').forEach((el) => (el.hidden = !state[el.dataset.show]));
      document.querySelectorAll('[data-hide]').forEach((el) => (el.hidden = !!state[el.dataset.hide]));
      document.querySelectorAll('[data-when]').forEach((el) => { const [k, v] = pair(el.dataset.when); el.hidden = state[k] !== v; });
      document.querySelectorAll('[data-pressed]').forEach((el) => { const [k, v] = pair(el.dataset.pressed); el.setAttribute('aria-pressed', String(state[k] === v)); });
      document.querySelectorAll('[data-expanded]').forEach((el) => el.setAttribute('aria-expanded', String(!!state[el.dataset.expanded])));
    };
    document.addEventListener('click', (e) => {
      const t = e.target.closest('[data-toggle],[data-open],[data-close],[data-set],[data-call]');
      if (!t) return;
      const { toggle, open, close, set, call } = t.dataset;
      if (call) actions[call]?.(e);
      if (toggle) state[toggle] = !state[toggle];
      if (open) state[open] = true;
      if (close) state[close] = false;
      if (set) { const [k, v] = pair(set); state[k] = v; }
      sync();
    });
    sync();
  })();
</script>

/* theme.css — brand color #4f46e5 for Bootstrap 5.3 */
:root { --brand: #4f46e5; --brand-hover: #433cc3; --brand-rgb: 79, 70, 229; --brand-contrast: #ffffff; }
.btn-brand {
  --bs-btn-color: var(--brand-contrast); --bs-btn-bg: var(--brand); --bs-btn-border-color: var(--brand);
  --bs-btn-hover-color: var(--brand-contrast); --bs-btn-hover-bg: var(--brand-hover); --bs-btn-hover-border-color: var(--brand-hover);
  --bs-btn-active-color: var(--brand-contrast); --bs-btn-active-bg: var(--brand-hover); --bs-btn-active-border-color: var(--brand-hover);
  --bs-btn-focus-shadow-rgb: var(--brand-rgb);
}
.text-brand { color: var(--brand) !important; }
.border-brand { border: 2px solid var(--brand) !important; }
.bg-brand-subtle { background-color: rgba(var(--brand-rgb), .12) !important; }
.form-control:focus, .form-check-input:focus { border-color: var(--brand); box-shadow: 0 0 0 .25rem rgba(var(--brand-rgb), .25); }
.form-check-input:checked { background-color: var(--brand); border-color: var(--brand); }
.overlay { background: rgba(15, 23, 42, .5); backdrop-filter: blur(4px); z-index: 1050; }
.choice[aria-pressed="true"] { border-color: var(--brand) !important; color: var(--brand) !important; box-shadow: 0 0 0 .2rem rgba(var(--brand-rgb), .2); }
.mw-sm { max-width: 24rem; } .mw-md { max-width: 28rem; } .mw-lg { max-width: 32rem; } .mw-xl { max-width: 36rem; }
.mw-2xl { max-width: 42rem; } .mw-4xl { max-width: 56rem; } .mw-6xl { max-width: 72rem; }