/* ==========================================================================
   DESIGN TOKENS & SYSTEM VARIABLES
   Tuân thủ tiêu chuẩn kỹ thuật kt-coder-agent & kt-frontend-landing
   ========================================================================== */

:root {
  /* Color Palette - Sang trọng, độ tương phản cao chuẩn WCAG */
  --color-bg: #0d0f12;
  --color-surface: #14171d;
  --color-surface-elevated: #1b2028;
  --color-surface-card: rgba(27, 32, 40, 0.7);
  --color-border: rgba(255, 255, 255, 0.08);
  --color-border-hover: rgba(255, 255, 255, 0.2);

  --color-text-primary: #f8fafc;
  --color-text-secondary: #94a3b8;
  --color-text-muted: #64748b;
  --color-text-inverse: #090a0d;

  /* Accent & Conversion CTA Color (Vàng Gold / Hổ phách nổi bật) */
  --color-primary: #eab308;
  --color-primary-hover: #facc15;
  --color-primary-glow: rgba(234, 179, 8, 0.25);
  
  --color-success: #10b981;
  --color-badge-bg: rgba(234, 179, 8, 0.12);
  --color-badge-text: #fde047;

  /* Typography */
  --font-family-base: 'Roboto', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  
  /* Fluid Type Scale (Desktop <-> Mobile) */
  --font-size-hero: clamp(2rem, 4.5vw + 1rem, 3.5rem);
  --font-size-h2: clamp(1.6rem, 3vw + 0.5rem, 2.4rem);
  --font-size-h3: clamp(1.2rem, 2vw + 0.3rem, 1.5rem);
  --font-size-body: clamp(0.95rem, 0.3vw + 0.85rem, 1.05rem);
  --font-size-sm: 0.875rem;
  --font-size-xs: 0.75rem;

  --line-height-tight: 1.15;
  --line-height-snug: 1.35;
  --line-height-normal: 1.6;

  /* Spacing Rhythm */
  --pad-x: clamp(1rem, 4vw, 2.5rem);
  --section-spacing-y: clamp(3.5rem, 7vw, 6.5rem);
  --max-content-width: 1200px;
  --max-readable-width: 760px;

  /* Radius & Shadows */
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-full: 9999px;

  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.25);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.35);
  --shadow-lg: 0 20px 40px rgba(0, 0, 0, 0.5);
  --shadow-cta: 0 4px 20px var(--color-primary-glow);

  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
  --transition-slow: 0.4s cubic-bezier(0.16, 1, 0.3, 1);
}

/* ==========================================================================
   RESET & BASE STYLES
   ========================================================================== */

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  text-size-adjust: 100%;
  -webkit-text-size-adjust: 100%;
  font-family: var(--font-family-base);
  background-color: var(--color-bg);
  color: var(--color-text-primary);
  line-height: var(--line-height-normal);
}

body {
  min-height: 100vh;
  overflow-x: hidden;
  position: relative;
}

img, svg, picture, video {
  max-width: 100%;
  display: block;
  height: auto;
}

a {
  color: inherit;
  text-decoration: none;
}

button, input, textarea, select {
  font: inherit;
  color: inherit;
}

ul, ol {
  list-style: none;
}

/* ==========================================================================
   LAYOUT CONTAINERS & UTILITIES
   ========================================================================== */

.container {
  width: 100%;
  max-width: var(--max-content-width);
  margin-left: auto;
  margin-right: auto;
  padding-left: var(--pad-x);
  padding-right: var(--pad-x);
  min-width: 0;
}

.section {
  padding-top: var(--section-spacing-y);
  padding-bottom: var(--section-spacing-y);
  position: relative;
}

.section--alt {
  background-color: var(--color-surface);
}

.section-header {
  text-align: center;
  max-width: var(--max-readable-width);
  margin: 0 auto clamp(2rem, 4vw, 3.5rem);
}

.section-tag {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: var(--font-size-xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  padding: 0.35rem 0.85rem;
  border-radius: var(--radius-full);
  background: var(--color-badge-bg);
  color: var(--color-badge-text);
  border: 1px solid rgba(234, 179, 8, 0.25);
  margin-bottom: 1rem;
}

.section-title {
  font-size: var(--font-size-h2);
  line-height: var(--line-height-tight);
  font-weight: 800;
  margin-bottom: 1rem;
  letter-spacing: -0.02em;
}

.section-subtitle {
  font-size: var(--font-size-body);
  color: var(--color-text-secondary);
  line-height: var(--line-height-normal);
}

/* Highlight text */
.highlight-text {
  color: var(--color-primary);
  background: linear-gradient(90deg, #facc15, #f59e0b);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

/* ==========================================================================
   CTA BUTTON SYSTEM (Chuẩn CRO)
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.6rem;
  font-weight: 700;
  font-size: 1rem;
  padding: 0.95rem 1.85rem;
  border-radius: var(--radius-full);
  border: none;
  cursor: pointer;
  transition: all var(--transition-normal);
  white-space: normal;
  text-align: center;
  user-select: none;
}

.btn-primary {
  background: linear-gradient(135deg, #facc15 0%, #eab308 100%);
  color: var(--color-text-inverse);
  box-shadow: var(--shadow-cta);
}

.btn-primary:hover {
  transform: translateY(-2px);
  background: linear-gradient(135deg, #fde047 0%, #facc15 100%);
  box-shadow: 0 6px 24px rgba(234, 179, 8, 0.4);
}

.btn-primary:active {
  transform: translateY(0);
}

.btn-secondary {
  background: var(--color-surface-elevated);
  color: var(--color-text-primary);
  border: 1px solid var(--color-border);
}

.btn-secondary:hover {
  border-color: var(--color-border-hover);
  background: rgba(255, 255, 255, 0.08);
}

.btn-sm {
  padding: 0.55rem 1.1rem;
  font-size: var(--font-size-sm);
}

.btn-full {
  width: 100%;
}

.btn-icon {
  width: 1.25rem;
  height: 1.25rem;
  transition: transform var(--transition-fast);
}

.btn:hover .btn-icon {
  transform: translateX(3px);
}

/* ==========================================================================
   HEADER / NAVBAR
   ========================================================================== */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  background: rgba(13, 15, 18, 0.85);
  border-bottom: 1px solid var(--color-border);
  padding: 0.85rem 0;
}

.nav-wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 800;
  font-size: 1.15rem;
  letter-spacing: -0.01em;
}

.brand-badge {
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  background: var(--color-primary);
  color: var(--color-text-inverse);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 900;
}

/* ==========================================================================
   HERO SECTION
   ========================================================================== */

.hero {
  padding-top: clamp(2.5rem, 5vw, 5rem);
  padding-bottom: clamp(3rem, 6vw, 6rem);
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: clamp(2rem, 5vw, 4rem);
  align-items: center;
}

.hero-content {
  min-width: 0;
}

.hero-title {
  font-size: var(--font-size-hero);
  line-height: var(--line-height-tight);
  font-weight: 900;
  letter-spacing: -0.03em;
  margin-bottom: 1.25rem;
}

.hero-description {
  font-size: clamp(1rem, 1.2vw, 1.15rem);
  color: var(--color-text-secondary);
  line-height: var(--line-height-normal);
  margin-bottom: 1.75rem;
  max-width: 600px;
}

.hero-bullets {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  margin-bottom: 2rem;
}

.hero-bullet-item {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  font-size: var(--font-size-body);
  color: var(--color-text-primary);
}

.check-icon {
  width: 18px;
  height: 18px;
  color: var(--color-success);
  flex-shrink: 0;
}

.hero-cta-group {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.hero-proof {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
}

.avatar-group {
  display: flex;
}

.avatar-group span {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: 2px solid var(--color-bg);
  margin-left: -8px;
  background-color: var(--color-surface-elevated);
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 10px;
  color: var(--color-text-secondary);
}

.avatar-group span:first-child {
  margin-left: 0;
}

/* Hero Visual / Mockup Box */
.hero-visual {
  min-width: 0;
  position: relative;
}

.mockup-card {
  position: relative;
  background: var(--color-surface-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-lg);
  overflow: hidden;
}

.mockup-card::before {
  content: '';
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle, var(--color-primary-glow) 0%, transparent 60%);
  pointer-events: none;
  opacity: 0.6;
}

.mockup-inner {
  position: relative;
  z-index: 1;
}

.mockup-aspect {
  aspect-ratio: 4 / 3;
  background: var(--color-surface-elevated);
  border-radius: var(--radius-md);
  border: 1px dashed var(--color-border);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 1.5rem;
  text-align: center;
  color: var(--color-text-secondary);
}

/* ==========================================================================
   PROBLEM & AGITATION SECTION
   ========================================================================== */

.cards-grid-3 {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 1.5rem;
}

.card {
  background: var(--color-surface-card);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 1.75rem;
  transition: transform var(--transition-fast), border-color var(--transition-fast);
  min-width: 0;
}

.card:hover {
  transform: translateY(-4px);
  border-color: var(--color-border-hover);
}

.card-icon {
  width: 44px;
  height: 44px;
  border-radius: var(--radius-sm);
  background: rgba(239, 68, 68, 0.15);
  color: #f87171;
  display: flex;
  align-items: center;
  justify-content: center;
  margin-bottom: 1.25rem;
}

.card-icon--success {
  background: rgba(16, 185, 129, 0.15);
  color: #34d399;
}

.card-title {
  font-size: var(--font-size-h3);
  font-weight: 700;
  margin-bottom: 0.75rem;
  line-height: var(--line-height-snug);
}

.card-desc {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
  line-height: var(--line-height-normal);
}

/* ==========================================================================
   OFFER STACK & PRICING
   ========================================================================== */

.offer-box {
  background: var(--color-surface-elevated);
  border: 2px solid var(--color-primary);
  border-radius: var(--radius-lg);
  padding: clamp(2rem, 4vw, 3rem);
  box-shadow: 0 0 35px var(--color-primary-glow);
  position: relative;
  max-width: 860px;
  margin: 0 auto;
}

.offer-badge {
  position: absolute;
  top: -14px;
  left: 50%;
  transform: translateX(-50%);
  background: var(--color-primary);
  color: var(--color-text-inverse);
  font-size: var(--font-size-xs);
  font-weight: 800;
  text-transform: uppercase;
  padding: 0.35rem 1.25rem;
  border-radius: var(--radius-full);
}

.offer-grid {
  display: grid;
  grid-template-columns: 1.3fr 0.9fr;
  gap: 2.5rem;
  align-items: center;
}

.offer-stack-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.offer-item {
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
}

.offer-item-title {
  font-weight: 600;
  font-size: 1rem;
  color: var(--color-text-primary);
}

.offer-item-value {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
  text-decoration: line-through;
  margin-left: 0.5rem;
}

.pricing-panel {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: 2rem 1.5rem;
  text-align: center;
}

.price-original {
  font-size: 1.1rem;
  color: var(--color-text-muted);
  text-decoration: line-through;
  margin-bottom: 0.25rem;
}

.price-deal {
  font-size: clamp(2rem, 3.5vw, 2.75rem);
  font-weight: 900;
  color: var(--color-primary);
  line-height: 1;
  margin-bottom: 0.5rem;
}

.price-note {
  font-size: var(--font-size-xs);
  color: var(--color-text-secondary);
  margin-bottom: 1.5rem;
}

/* ==========================================================================
   FAQ ACCORDION
   ========================================================================== */

.faq-list {
  max-width: var(--max-readable-width);
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
}

.faq-item {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.faq-item.active {
  border-color: var(--color-primary);
}

.faq-question {
  width: 100%;
  background: none;
  border: none;
  text-align: left;
  padding: 1.25rem 1.5rem;
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--color-text-primary);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  cursor: pointer;
}

.faq-arrow {
  width: 20px;
  height: 20px;
  color: var(--color-text-secondary);
  transition: transform var(--transition-normal);
  flex-shrink: 0;
}

.faq-item.active .faq-arrow {
  transform: rotate(180deg);
  color: var(--color-primary);
}

.faq-answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height var(--transition-slow);
  padding: 0 1.5rem;
  color: var(--color-text-secondary);
  font-size: var(--font-size-body);
}

.faq-answer-inner {
  padding-bottom: 1.25rem;
  line-height: var(--line-height-normal);
}

/* ==========================================================================
   MODAL POPUP (Lead Form / Order)
   ========================================================================== */

.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.75);
  backdrop-filter: blur(6px);
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
  opacity: 0;
  visibility: hidden;
  transition: opacity var(--transition-normal), visibility var(--transition-normal);
}

.modal-backdrop.open {
  opacity: 1;
  visibility: visible;
}

.modal-card {
  background: var(--color-surface-elevated);
  border: 1px solid var(--color-border-hover);
  border-radius: var(--radius-lg);
  max-width: 500px;
  width: 100%;
  padding: clamp(1.5rem, 3vw, 2.25rem);
  box-shadow: var(--shadow-lg);
  position: relative;
  transform: scale(0.96) translateY(10px);
  transition: transform var(--transition-normal);
  max-height: 90vh;
  overflow-y: auto;
}

.modal-backdrop.open .modal-card {
  transform: scale(1) translateY(0);
}

.modal-close {
  position: absolute;
  top: 1rem;
  right: 1rem;
  background: none;
  border: none;
  color: var(--color-text-muted);
  cursor: pointer;
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  transition: color var(--transition-fast), background-color var(--transition-fast);
}

.modal-close:hover {
  color: var(--color-text-primary);
  background-color: rgba(255, 255, 255, 0.1);
}

.form-group {
  margin-bottom: 1rem;
  text-align: left;
}

.form-label {
  display: block;
  font-size: var(--font-size-sm);
  font-weight: 600;
  margin-bottom: 0.35rem;
  color: var(--color-text-primary);
}

.form-input {
  width: 100%;
  padding: 0.8rem 1rem;
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  color: var(--color-text-primary);
  outline: none;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.form-input:focus {
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px var(--color-primary-glow);
}

/* ==========================================================================
   FOOTER
   ========================================================================== */

.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 2.5rem 0;
  background: var(--color-surface);
  color: var(--color-text-muted);
  font-size: var(--font-size-sm);
  text-align: center;
}

.footer-content {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.75rem;
}

/* ==========================================================================
   RESPONSIVE MEDIA QUERIES (Mobile-first QA: 390px / 768px / 1024px)
   ========================================================================== */

@media (max-width: 900px) {
  .hero-grid {
    grid-template-columns: 1fr;
    text-align: center;
  }

  .hero-description {
    margin-left: auto;
    margin-right: auto;
  }

  .hero-bullets {
    align-items: center;
  }

  .hero-cta-group {
    justify-content: center;
  }

  .hero-proof {
    justify-content: center;
  }

  .offer-grid {
    grid-template-columns: 1fr;
    gap: 2rem;
  }
}

@media (max-width: 480px) {
  .btn {
    width: 100%;
  }

  .hero-cta-group {
    flex-direction: column;
    width: 100%;
  }

  .nav-cta {
    display: none;
  }
}