/* ==========================================================================
   Shared public header — source of truth: homepage `.nav`
   Load after page-specific CSS so these rules win over blog/guide headers.
   Self-contained tokens so blog/guide need not import tokens.css
   (tokens.css resets lists/margins and would restyle article bodies).
   ========================================================================== */

:root {
  --paper: #F8FAFC;
  --panel: #FFFFFF;
  --panel-2: #F1F5F9;
  --card: #FFFFFF;
  --ink: #0F172A;
  --ink-2: #334155;
  --muted: #64748B;
  --muted-2: #475569;
  --line: #E2E8F0;
  --line-soft: #F1F5F9;
  --volt: #1D6AE5;
  --fail: #DC2626;
  --pass-ink: #047857;
  --acid: #ECFDF5;
  --font-display: 'Sora', sans-serif;
  --sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans TC', 'Noto Sans SC', 'PingFang TC', 'Microsoft JhengHei', sans-serif;
  --radius-sm: 6px;
  --radius-md: 10px;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.12);
  --ease-out: cubic-bezier(.16, 1, .3, 1);
  --shell: 1200px;
  --nav-h: 60px;
}

.shell {
  width: min(var(--shell), 100% - 48px);
  margin-inline: auto;
}

.nav {
  position: sticky;
  top: 0; left: 0; right: 0;
  z-index: 40;
  height: var(--nav-h);
  background: rgba(248, 250, 252, .85);
  -webkit-backdrop-filter: blur(12px);
  backdrop-filter: blur(12px);
  transition: box-shadow .3s var(--ease-out), border-color .3s var(--ease-out);
  border-bottom: 1px solid transparent;
}
.nav__in {
  height: var(--nav-h);
  display: flex;
  align-items: center;
  gap: 28px;
}
.nav a {
  color: inherit;
  text-decoration: none;
}
.nav a:hover { text-decoration: none; }
.nav__logo {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  text-decoration: none;
  font-family: var(--sans);
  font-weight: 700;
  font-size: 14px;
  letter-spacing: -.01em;
  color: var(--ink);
}
.nav__mark {
  width: 26px;
  height: 26px;
  flex-shrink: 0;
  display: grid;
  place-items: center;
  color: var(--volt);
}
.nav__mark svg {
  display: block;
  width: 100%;
  height: 100%;
  max-width: none;
}
.nav__links {
  display: flex;
  align-items: center;
  gap: 22px;
  margin-left: 12px;
}
.nav__links a {
  text-decoration: none;
  font-family: var(--sans);
  font-size: 12.5px;
  font-weight: 500;
  color: var(--muted-2);
  transition: color .18s var(--ease-out);
}
.nav__links a:hover { color: var(--ink); }
.nav__right {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 12px;
}

.nav .landing-header-actions { display: flex; align-items: center; gap: 8px; }
.nav .btn-login {
  padding: 8px 12px;
  border: 0;
  background: none;
  font-family: var(--sans);
  font-size: 12.5px;
  font-weight: 600;
  color: var(--ink-2);
  cursor: pointer;
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: color .18s var(--ease-out), background .18s var(--ease-out);
}
.nav .btn-login:hover { color: var(--ink); background: var(--panel-2); text-decoration: none; }
.nav .btn-signup {
  display: inline-flex;
  align-items: center;
  padding: 8px 14px;
  border: 1px solid transparent;
  border-radius: var(--radius-md);
  background: linear-gradient(135deg, #1D6AE5, #0EA5E9);
  color: #fff;
  font-family: var(--sans);
  font-size: 12.5px;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
  transition: filter .18s var(--ease-out), transform .18s var(--ease-out);
}
.nav .btn-signup:hover { filter: brightness(1.05); color: #fff; text-decoration: none; }
.nav .btn-signup:active { transform: translateY(1px); }

.nav__burger {
  display: none;
  width: 36px; height: 36px;
  padding: 0;
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  background: var(--card);
  cursor: pointer;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
}
.nav__burger span {
  display: block;
  width: 16px; height: 1.5px;
  background: var(--ink);
  transition: transform .2s var(--ease-out), opacity .2s var(--ease-out);
}
.nav__burger[aria-expanded="true"] span:nth-child(1) { transform: translateY(5.5px) rotate(45deg); }
.nav__burger[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav__burger[aria-expanded="true"] span:nth-child(3) { transform: translateY(-5.5px) rotate(-45deg); }

.nav.is-stuck {
  border-bottom-color: var(--line);
  box-shadow: var(--shadow-sm);
}
.nav.is-stuck .nav__links a { color: var(--muted-2); }
.nav.is-stuck .nav__links a:hover { color: var(--ink); }

/* Auth modal — same flow as /js/landing.js */
.auth-modal { position: fixed; inset: 0; display: flex; align-items: center; justify-content: center; z-index: 60; }
.auth-modal.hidden { display: none; }
.auth-modal-backdrop { position: fixed; inset: 0; background: rgba(10, 22, 40, .7); backdrop-filter: blur(3px); }
.auth-modal-content {
  position: relative;
  z-index: 10;
  background: var(--panel);
  border-radius: 20px;
  padding: 40px;
  width: calc(100% - 48px);
  max-width: 24rem;
  box-shadow: var(--shadow-lg);
  text-align: center;
}
.auth-modal-content h3 { font-family: var(--font-display); font-size: 20px; font-weight: 700; margin: 0 0 8px; color: var(--ink); }
.auth-modal-content p { font-size: 14px; color: var(--muted-2); margin: 0 0 20px; }
.auth-btn-google {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
  width: 100%;
  padding: 12px;
  border-radius: var(--radius-md);
  border: 1px solid var(--line);
  background: var(--panel);
  color: var(--ink);
  font-family: var(--sans);
  font-weight: 600;
  font-size: 14px;
  cursor: pointer;
  transition: background .18s var(--ease-out), box-shadow .18s var(--ease-out);
}
.auth-btn-google:hover { background: var(--panel-2); box-shadow: var(--shadow-sm); }
.auth-error { color: var(--fail); background: #FEF2F2; border-radius: var(--radius-sm); padding: 8px 12px; font-size: 12px; margin: 8px 0 0; }
.auth-info { color: var(--pass-ink); background: var(--acid); border-radius: var(--radius-sm); padding: 8px 12px; font-size: 12px; margin: 8px 0 0; }
.auth-error.hidden, .auth-info.hidden { display: none; }
.auth-modal-close {
  position: absolute;
  top: 16px; right: 16px;
  width: 2rem; height: 2rem;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--muted);
  cursor: pointer;
  border: none;
  background: none;
  transition: color .18s var(--ease-out), background .18s var(--ease-out);
}
.auth-modal-close:hover { color: var(--ink); background: var(--panel-2); }

@media (max-width: 900px) {
  .nav__links {
    display: none;
    position: absolute;
    top: var(--nav-h);
    left: 0; right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    margin-left: 0;
    padding: 8px 24px 16px;
    background: var(--panel);
    border-bottom: 1px solid var(--line);
    box-shadow: var(--shadow-md);
  }
  .nav__links.is-open { display: flex; }
  .nav__links a {
    padding: 12px 0;
    font-size: 14px;
    border-bottom: 1px solid var(--line-soft);
  }
  .nav__links a:last-child { border-bottom: 0; }
  .nav__burger { display: inline-flex; }
  .nav__in { gap: 16px; }
}

@media (max-width: 520px) {
  .nav__logo-text { display: none; }
  .nav .btn-login { padding: 8px 8px; }
  .nav .btn-signup { padding: 8px 12px; }
  .auth-modal-content { padding: 32px 24px; }
}

@media (pointer: coarse) {
  .nav .btn-login, .nav .btn-signup, .auth-btn-google { min-height: 44px; }
  .nav .btn-login { padding: 10px 14px; }
  .nav .btn-signup { padding: 10px 18px; }
  .nav__links a { display: flex; align-items: center; min-height: 48px; }
}

@media (prefers-reduced-motion: reduce) {
  .nav, .nav__links a, .nav .btn-login, .nav .btn-signup,
  .nav__burger span, .auth-btn-google, .auth-modal-close {
    transition-duration: .001ms !important;
  }
}