/* ====================================================================
   LingLang Landing Page — Cognitive Sanctuary Theme
   ==================================================================== */

/* --- Navigation --- */
.landing-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  padding: var(--space-4) 0;
  background: transparent;
  transition: background var(--transition-base), backdrop-filter var(--transition-base);
}
.landing-nav.nav-scrolled {
  background: rgba(11, 19, 38, 0.85);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid rgba(69, 70, 77, 0.15);
}

.nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--space-8);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-family: var(--font-display);
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--on-surface);
  text-decoration: none;
  letter-spacing: -0.02em;
}
.nav-logo:hover { color: var(--primary); }

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-6);
}
.nav-links a {
  color: var(--on-surface-variant);
  font-size: 0.9rem;
  font-weight: 500;
  text-decoration: none;
  transition: color var(--transition-fast);
}
.nav-links a:hover { color: var(--primary); }

.nav-dashboard-btn {
  padding: var(--space-2) var(--space-5) !important;
  font-size: 0.85rem !important;
}

/* --- Hero --- */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  background: var(--surface);
}

#hero-canvas {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 1;
}

.hero-overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: radial-gradient(ellipse at center, transparent 0%, var(--surface) 70%);
  z-index: 2;
  pointer-events: none;
}

.hero-content {
  position: relative;
  z-index: 3;
  max-width: 800px;
  padding: var(--space-24) var(--space-8);
  text-align: center;
}

.hero-badge {
  display: inline-block;
  padding: var(--space-1) var(--space-4);
  background: rgba(180, 197, 255, 0.1);
  color: var(--primary);
  border-radius: var(--radius-xl);
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: var(--space-6);
}

.hero-title {
  font-size: clamp(2.5rem, 5vw, 4rem);
  font-weight: 800;
  line-height: 1.1;
  margin-bottom: var(--space-6);
  letter-spacing: -0.02em;
}

.hero-subtitle {
  font-size: 1.1rem;
  color: var(--on-surface-variant);
  line-height: 1.7;
  margin-bottom: var(--space-8);
}

.hero-cta-group {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-3);
}
.hero-cta { font-size: 1.1rem; padding: var(--space-4) var(--space-10); }
.hero-cta-note { font-size: 0.85rem; }

.email-form {
  display: none;
  flex-direction: row;
  align-items: center;
  gap: var(--space-3);
  flex-wrap: wrap;
  justify-content: center;
}
.email-form.active { display: flex; }

.email-input {
  background: var(--surface-well);
  color: var(--on-surface);
  border: none;
  border-radius: var(--radius-sm);
  padding: var(--space-3) var(--space-4);
  font-size: 1rem;
  font-family: var(--font-body);
  width: 280px;
  outline: none;
  transition: box-shadow var(--transition-fast);
}
.email-input:focus {
  box-shadow: 0 0 0 2px var(--tertiary);
}
.email-input::placeholder {
  color: var(--on-surface-muted);
}

.email-status {
  width: 100%;
  text-align: center;
  font-size: 0.9rem;
  margin-top: var(--space-2);
  min-height: 1.4em;
}
.email-status.success { color: var(--secondary); }
.email-status.error { color: var(--error); }

/* --- Section Shared --- */
.section-header {
  margin-bottom: var(--space-12);
}
.section-tag {
  display: inline-block;
  padding: var(--space-1) var(--space-3);
  background: rgba(123, 208, 255, 0.1);
  color: var(--tertiary);
  border-radius: var(--radius-xl);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-bottom: var(--space-4);
}
.section-title {
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 800;
  letter-spacing: -0.02em;
}
.section-subtitle {
  font-size: 1.1rem;
  margin-top: var(--space-4);
  max-width: 600px;
}

/* --- How It Works --- */
.how-it-works {
  background: var(--surface-low);
}

.steps-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-6);
}
@media (max-width: 768px) {
  .steps-grid { grid-template-columns: 1fr; }
}

.step-card {
  position: relative;
  padding-top: var(--space-10);
}
.step-number {
  position: absolute;
  top: var(--space-6);
  right: var(--space-6);
  font-size: 3rem;
  font-weight: 800;
  color: var(--surface-top);
  opacity: 0.5;
  line-height: 1;
}
.step-icon {
  font-size: 2rem;
  margin-bottom: var(--space-4);
}
.step-title {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: var(--space-3);
}
.step-desc {
  font-size: 0.95rem;
  color: var(--on-surface-variant);
  line-height: 1.7;
}

/* --- Feature Sections --- */
.feature-section {
  background: var(--surface);
}
.feature-alt {
  background: var(--surface-low);
}

.feature-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-16);
  align-items: center;
}
.feature-grid-reverse {
  grid-template-columns: 1fr 1fr;
  direction: ltr;
}
@media (max-width: 900px) {
  .feature-grid, .feature-grid-reverse {
    grid-template-columns: 1fr;
    gap: var(--space-10);
  }
}

.feature-visual {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 300px;
}

.feature-text {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.feature-tag {
  display: inline-block;
  padding: var(--space-1) var(--space-3);
  background: rgba(123, 208, 255, 0.1);
  color: var(--tertiary);
  border-radius: var(--radius-xl);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  align-self: flex-start;
}

.feature-title {
  font-size: clamp(1.5rem, 3vw, 2.2rem);
  font-weight: 800;
  letter-spacing: -0.02em;
}

.feature-desc {
  font-size: 0.95rem;
  color: var(--on-surface-variant);
  line-height: 1.8;
}

.feature-stats {
  display: flex;
  gap: var(--space-8);
  margin-top: var(--space-4);
}
.stat {
  display: flex;
  flex-direction: column;
}
.stat-value {
  font-size: 1.8rem;
  font-weight: 700;
  line-height: 1.2;
}
.stat-label {
  font-size: 0.8rem;
}

/* --- FSRS Diagram --- */
.fsrs-diagram {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  width: 100%;
  padding: var(--space-6);
}
.fsrs-states-row {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  flex-wrap: wrap;
}
.fsrs-lapse-row {
  margin-left: var(--space-12);
}
.fsrs-state {
  background: var(--surface-high);
  border-radius: var(--radius-md);
  padding: var(--space-3) var(--space-5);
  text-align: center;
  min-width: 100px;
}
.fsrs-state-label {
  display: block;
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 0.95rem;
  margin-bottom: var(--space-1);
}
.fsrs-state-sub {
  display: block;
  font-size: 0.75rem;
  color: var(--on-surface-muted);
}
.fsrs-new .fsrs-state-label { color: var(--tertiary); }
.fsrs-learning .fsrs-state-label { color: var(--primary); }
.fsrs-review .fsrs-state-label { color: var(--secondary); }
.fsrs-relearning .fsrs-state-label { color: var(--error); }

.fsrs-arrow-right {
  color: var(--on-surface-muted);
  font-size: 1.2rem;
}
.fsrs-arrow-up {
  color: var(--error);
  font-size: 1rem;
  transform: rotate(-90deg);
}

.fsrs-grades {
  background: var(--surface-well);
  border-radius: var(--radius-md);
  padding: var(--space-4);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  margin-top: var(--space-4);
}
.grade-row {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-size: 0.9rem;
}
.grade-grade {
  width: 28px;
  height: 28px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  font-size: 0.85rem;
  font-weight: 700;
  flex-shrink: 0;
}
.grade-again { background: rgba(255, 180, 171, 0.2); color: var(--error); }
.grade-hard { background: rgba(255, 180, 171, 0.1); color: var(--error); }
.grade-good { background: rgba(78, 222, 163, 0.15); color: var(--secondary); }
.grade-easy { background: rgba(78, 222, 163, 0.25); color: var(--secondary); }

.grade-arrow { color: var(--on-surface-muted); }
.grade-target { color: var(--on-surface-variant); }

/* --- Ripple Visual --- */
.ripple-visual {
  width: 100%;
  max-width: 440px;
}
#ripple-canvas {
  width: 100%;
  height: auto;
  border-radius: var(--radius-md);
}

/* --- Agent Flow --- */
.agent-visual {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-6);
}
.agent-flow {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  flex-wrap: wrap;
  justify-content: center;
}
.agent-node {
  background: var(--surface-low);
  border-radius: var(--radius-md);
  padding: var(--space-4) var(--space-5);
  text-align: center;
  min-width: 90px;
  transition: all var(--transition-base);
}
.agent-node:hover {
  background: var(--surface-high);
  transform: translateY(-2px);
}
.agent-node-icon {
  font-size: 1.5rem;
  margin-bottom: var(--space-2);
}
.agent-node-label {
  font-size: 0.85rem;
  font-weight: 700;
}
.agent-node-sub {
  font-size: 0.7rem;
  margin-top: var(--space-1);
}

.agent-arrow {
  color: var(--on-surface-muted);
  font-size: 1.2rem;
}

.agent-processor {
  border-left: 3px solid var(--tertiary);
}
.agent-supervisor {
  border-left: 3px solid var(--primary);
}
.agent-tutor {
  border-left: 3px solid var(--secondary);
}

.agent-loop {
  margin-top: var(--space-4);
  padding: var(--space-3) var(--space-5);
  background: var(--surface-well);
  border-radius: var(--radius-sm);
}
.agent-loop-label {
  font-size: 0.75rem;
  letter-spacing: 0.03em;
}

/* --- Privacy Section --- */
.privacy-section {
  background: var(--surface-low);
}
.privacy-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-6);
}
@media (max-width: 768px) {
  .privacy-grid { grid-template-columns: 1fr; }
}

.privacy-card {
  text-align: center;
  padding: var(--space-8) var(--space-6);
}
.privacy-icon {
  font-size: 2.5rem;
  margin-bottom: var(--space-4);
}
.privacy-title {
  font-size: 1.1rem;
  margin-bottom: var(--space-3);
}
.privacy-desc {
  font-size: 0.9rem;
  color: var(--on-surface-variant);
  line-height: 1.7;
}

/* --- Languages --- */
.languages-section {
  background: var(--surface);
}

.language-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-6);
  margin-top: var(--space-10);
}
@media (max-width: 900px) {
  .language-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 600px) {
  .language-grid { grid-template-columns: 1fr; }
}

.lang-card {
  padding: var(--space-6);
  cursor: default;
}
.lang-flag {
  font-size: 2rem;
  display: block;
  margin-bottom: var(--space-3);
}
.lang-name {
  font-size: 1.15rem;
  font-weight: 700;
  margin-bottom: var(--space-2);
}
.lang-persona {
  font-size: 0.9rem;
  color: var(--on-surface-variant);
  margin-bottom: var(--space-2);
  font-style: italic;
}
.lang-greeting {
  font-size: 0.85rem;
  color: var(--on-surface-muted);
  margin-bottom: var(--space-3);
}
.lang-ratio {
  display: inline-block;
  padding: var(--space-1) var(--space-3);
  background: rgba(78, 222, 163, 0.1);
  color: var(--secondary);
  border-radius: var(--radius-xl);
  font-size: 0.7rem;
  letter-spacing: 0.05em;
}

/* --- CTA Section --- */
.cta-section {
  background: var(--surface-low);
  text-align: center;
  padding: var(--space-24) var(--space-8);
}
.cta-title {
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 800;
  margin-bottom: var(--space-4);
}
.cta-subtitle {
  margin-bottom: var(--space-8);
  font-size: 1.1rem;
}
.cta-button {
  font-size: 1.1rem;
  padding: var(--space-4) var(--space-10);
}

/* --- Footer --- */
.landing-footer {
  background: var(--surface-well);
  padding: var(--space-10) 0;
  border-top: 1px solid rgba(69, 70, 77, 0.1);
}
.footer-tech {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  flex-wrap: wrap;
  margin-bottom: var(--space-6);
}
.footer-tech-item {
  padding: var(--space-1) var(--space-3);
  background: var(--surface-high);
  border-radius: var(--radius-xl);
  font-size: 0.8rem;
  color: var(--on-surface-variant);
  font-family: var(--font-mono);
}
.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--space-4);
}
.footer-link {
  font-size: 0.85rem;
}

/* --- Scroll animations --- */
.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}
.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Stagger children */
.steps-grid .reveal:nth-child(2) { transition-delay: 0.1s; }
.steps-grid .reveal:nth-child(3) { transition-delay: 0.2s; }
.language-grid .reveal:nth-child(2) { transition-delay: 0.08s; }
.language-grid .reveal:nth-child(3) { transition-delay: 0.16s; }
.language-grid .reveal:nth-child(4) { transition-delay: 0.24s; }
.language-grid .reveal:nth-child(5) { transition-delay: 0.32s; }
.language-grid .reveal:nth-child(6) { transition-delay: 0.40s; }
.privacy-grid .reveal:nth-child(2) { transition-delay: 0.1s; }
.privacy-grid .reveal:nth-child(3) { transition-delay: 0.2s; }

/* --- Responsive --- */
@media (max-width: 768px) {
  .nav-links { display: none; }
  .feature-grid, .feature-grid-reverse {
    grid-template-columns: 1fr;
  }
  .hero-title { font-size: 2rem; }
  .hero-subtitle { font-size: 0.95rem; }
  .feature-visual { margin-bottom: var(--space-6); }
  .feature-grid-reverse .feature-visual { order: -1; }
  .section-inner { padding: var(--space-12) var(--space-5); }
}