/* ============================================================
   Yuan Sheng — Dark Luxury / Premium
   北京元生腾远科技有限公司
   ============================================================ */

/* --- Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Playfair+Display:ital,wght@0,400;0,500;0,600;0,700;1,400;1,500&family=Inter:wght@200;300;400;500&display=swap');

/* --- Reset & Base --- */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --bg: #0A0A0A;
  --surface: #1A1A1A;
  --surface-hover: #222222;
  --gold: #C9A96E;
  --gold-dark: #8B6914;
  --text: #F5F0E8;
  --text-muted: #A09888;
  --border: #2A2A2A;
  --border-gold: rgba(201, 169, 110, 0.25);
  --footer-bg: #050505;
  --font-heading: 'Playfair Display', Georgia, 'Times New Roman', serif;
  --font-body: 'Inter', 'Helvetica Neue', Arial, sans-serif;
  --max-width: 1200px;
  --transition: 0.35s cubic-bezier(0.25, 0.46, 0.45, 0.94);
}

html {
  font-size: 100%;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-body);
  font-size: 16px;
  font-weight: 300;
  line-height: 1.75;
  color: var(--text);
  background-color: var(--bg);
  overflow-x: hidden;
}

/* --- Typography --- */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: 500;
  line-height: 1.3;
  color: var(--text);
}

h1 { font-size: clamp(2.5rem, 5vw, 4.5rem); }
h2 { font-size: clamp(1.8rem, 3.5vw, 2.8rem); }
h3 { font-size: clamp(1.3rem, 2.5vw, 1.75rem); }

p {
  margin-bottom: 1.25rem;
}

a {
  color: var(--gold);
  text-decoration: none;
  transition: color var(--transition);
}

a:hover {
  color: var(--text);
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

/* --- Utility --- */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.section-label {
  display: inline-block;
  font-family: var(--font-body);
  font-size: 0.75rem;
  font-weight: 400;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 1rem;
}

/* --- Fade-in Animation --- */
.fade-in {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.8s ease-out, transform 0.8s ease-out;
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ============================================================
   Navigation
   ============================================================ */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(10, 10, 10, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
  transition: background var(--transition);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
  height: 72px;
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  text-decoration: none;
  color: var(--text);
  font-family: var(--font-heading);
  font-size: 1.35rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.nav-logo svg {
  width: 36px;
  height: 36px;
  flex-shrink: 0;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 2.5rem;
  list-style: none;
}

.nav-links a {
  font-family: var(--font-body);
  font-size: 0.8125rem;
  font-weight: 400;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--text-muted);
  text-decoration: none;
  padding: 0.25rem 0;
  position: relative;
  transition: color var(--transition);
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 0;
  height: 1px;
  background: var(--gold);
  transition: width var(--transition);
}

.nav-links a:hover,
.nav-links a:focus-visible {
  color: var(--text);
}

.nav-links a:hover::after,
.nav-links a:focus-visible::after {
  width: 100%;
}

/* Hamburger */
.hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  width: 40px;
  height: 40px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0;
  z-index: 1001;
}

.hamburger span {
  display: block;
  width: 22px;
  height: 1.5px;
  background: var(--text);
  margin: 3px 0;
  transition: transform var(--transition), opacity var(--transition);
  transform-origin: center;
}

.hamburger.active span:nth-child(1) {
  transform: translateY(4.5px) rotate(45deg);
}

.hamburger.active span:nth-child(2) {
  opacity: 0;
}

.hamburger.active span:nth-child(3) {
  transform: translateY(-4.5px) rotate(-45deg);
}

/* ============================================================
   Hero
   ============================================================ */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  background: var(--bg);
  overflow: hidden;
  padding: 6rem 1.5rem 4rem;
}

/* Ambient light effect */
.hero::before {
  content: '';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 70vw;
  height: 70vw;
  max-width: 900px;
  max-height: 900px;
  background: radial-gradient(ellipse at center, rgba(201, 169, 110, 0.06) 0%, rgba(201, 169, 110, 0.02) 35%, transparent 70%);
  pointer-events: none;
  z-index: 0;
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: 800px;
}

.hero-eyebrow {
  font-family: var(--font-body);
  font-size: 0.7rem;
  font-weight: 400;
  letter-spacing: 0.35em;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 1.5rem;
}

.hero-title {
  font-family: var(--font-heading);
  font-weight: 600;
  font-size: clamp(3rem, 7vw, 5.5rem);
  line-height: 1.1;
  color: var(--text);
  margin-bottom: 1.5rem;
  letter-spacing: -0.02em;
}

.hero-title em {
  font-style: italic;
  color: var(--gold);
}

.hero-underline {
  display: block;
  width: 60px;
  height: 1px;
  background: var(--gold);
  margin: 0 auto 2rem;
}

.hero-text {
  font-size: 1.15rem;
  font-weight: 300;
  color: var(--text-muted);
  max-width: 560px;
  margin: 0 auto;
  line-height: 1.8;
}

/* ============================================================
   Metrics
   ============================================================ */
.metrics {
  background: var(--bg);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  padding: 3.5rem 1.5rem;
}

.metrics-grid {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 3rem;
  max-width: var(--max-width);
  margin: 0 auto;
  flex-wrap: wrap;
}

.metric-item {
  text-align: center;
}

.metric-value {
  font-family: var(--font-heading);
  font-size: 3rem;
  font-weight: 600;
  color: var(--gold);
  line-height: 1;
  margin-bottom: 0.35rem;
}

.metric-label {
  font-size: 0.75rem;
  font-weight: 400;
  text-transform: uppercase;
  letter-spacing: 0.15em;
  color: var(--text-muted);
}

.metric-dot {
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--gold);
  flex-shrink: 0;
}

/* ============================================================
   Sections (shared)
   ============================================================ */
.section {
  padding: 7rem 1.5rem;
}

.section-header {
  text-align: center;
  margin-bottom: 4rem;
}

.section-title {
  font-family: var(--font-heading);
  font-weight: 500;
  color: var(--text);
  margin-bottom: 1rem;
}

.section-subtitle {
  font-size: 1.05rem;
  color: var(--text-muted);
  font-weight: 300;
  max-width: 540px;
  margin: 0 auto;
}

/* ============================================================
   Services
   ============================================================ */
.services {
  background: var(--bg);
}

.services-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 2px;
  max-width: var(--max-width);
  margin: 0 auto;
  background: var(--border);
}

.service-card {
  background: var(--surface);
  padding: 3rem 2rem;
  position: relative;
  transition: background var(--transition), box-shadow var(--transition);
}

.service-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 2rem;
  right: 2rem;
  height: 1px;
  background: var(--gold);
  opacity: 0.4;
  transition: opacity var(--transition), left var(--transition), right var(--transition);
}

.service-card:hover,
.service-card:focus-within {
  background: var(--surface-hover);
  box-shadow: inset 0 0 60px rgba(201, 169, 110, 0.03);
}

.service-card:hover::before,
.service-card:focus-within::before {
  opacity: 0.8;
  left: 1.5rem;
  right: 1.5rem;
}

.service-icon {
  font-size: 2rem;
  margin-bottom: 1.5rem;
  display: block;
  opacity: 0.9;
}

.service-title {
  font-family: var(--font-heading);
  font-size: 1.35rem;
  font-weight: 500;
  color: var(--text);
  margin-bottom: 0.75rem;
}

.service-desc {
  font-size: 0.925rem;
  color: var(--text-muted);
  font-weight: 300;
  line-height: 1.7;
}

/* ============================================================
   Philosophy
   ============================================================ */
.philosophy {
  background: var(--surface);
  padding: 7rem 1.5rem;
  text-align: center;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.philosophy-inner {
  max-width: 720px;
  margin: 0 auto;
}

.philosophy-quote {
  font-family: var(--font-heading);
  font-size: clamp(1.6rem, 3.5vw, 2.4rem);
  font-style: italic;
  font-weight: 400;
  color: var(--gold);
  line-height: 1.5;
  position: relative;
}

.philosophy-quote::before {
  content: '\201C';
  font-family: var(--font-heading);
  font-size: 5rem;
  color: var(--gold);
  opacity: 0.15;
  position: absolute;
  top: -2rem;
  left: -0.75rem;
  line-height: 1;
}

.philosophy-attribution {
  font-family: var(--font-body);
  font-size: 0.85rem;
  font-weight: 300;
  color: var(--text-muted);
  letter-spacing: 0.1em;
  margin-top: 2rem;
  text-transform: uppercase;
}

/* ============================================================
   Process
   ============================================================ */
.process {
  background: var(--bg);
}

.process-list {
  max-width: 640px;
  margin: 0 auto;
  list-style: none;
  position: relative;
}

.process-list::before {
  content: '';
  position: absolute;
  top: 8px;
  bottom: 8px;
  left: 5px;
  width: 1px;
  background: var(--border);
}

.process-item {
  padding-left: 2.5rem;
  padding-bottom: 2.5rem;
  position: relative;
}

.process-item:last-child {
  padding-bottom: 0;
}

.process-item::before {
  content: '';
  position: absolute;
  left: 0;
  top: 8px;
  width: 11px;
  height: 11px;
  border-radius: 50%;
  background: var(--gold);
  border: 2px solid var(--bg);
  z-index: 1;
}

.process-step {
  font-size: 0.7rem;
  font-weight: 400;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 0.3rem;
}

.process-title {
  font-family: var(--font-heading);
  font-size: 1.25rem;
  font-weight: 500;
  color: var(--text);
  margin-bottom: 0.4rem;
}

.process-desc {
  font-size: 0.925rem;
  color: var(--text-muted);
  font-weight: 300;
  line-height: 1.7;
}

/* ============================================================
   Expertise
   ============================================================ */
.expertise {
  background: var(--bg);
}

.expertise-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 3rem;
  max-width: var(--max-width);
  margin: 0 auto;
}

.expertise-col {
  padding-left: 1.5rem;
  border-left: 1px solid var(--gold);
}

.expertise-col h3 {
  font-family: var(--font-heading);
  font-size: 1.35rem;
  font-weight: 500;
  color: var(--text);
  margin-bottom: 1rem;
}

.expertise-col p {
  font-size: 0.95rem;
  color: var(--text-muted);
  font-weight: 300;
  line-height: 1.8;
}

/* ============================================================
   CTA
   ============================================================ */
.cta {
  background: var(--surface);
  text-align: center;
  padding: 7rem 1.5rem;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.cta-inner {
  max-width: 600px;
  margin: 0 auto;
}

.cta-title {
  font-family: var(--font-heading);
  font-size: clamp(1.8rem, 3.5vw, 2.5rem);
  font-weight: 500;
  color: var(--text);
  margin-bottom: 1rem;
}

.cta-text {
  font-size: 1.05rem;
  color: var(--text-muted);
  font-weight: 300;
  margin-bottom: 2.5rem;
}

.btn-outline {
  display: inline-block;
  padding: 0.85rem 2.75rem;
  font-family: var(--font-body);
  font-size: 0.8rem;
  font-weight: 400;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--gold);
  background: transparent;
  border: 1px solid var(--gold);
  cursor: pointer;
  transition: background var(--transition), color var(--transition), border-color var(--transition);
  text-decoration: none;
}

.btn-outline:hover,
.btn-outline:focus-visible {
  background: var(--gold);
  color: var(--bg);
  border-color: var(--gold);
}

/* ============================================================
   Contact
   ============================================================ */
.contact {
  background: var(--bg);
}

.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4rem;
  max-width: var(--max-width);
  margin: 0 auto;
}

.contact-info h3 {
  font-family: var(--font-heading);
  font-size: 1.5rem;
  font-weight: 500;
  color: var(--text);
  margin-bottom: 1.25rem;
}

.contact-info p {
  font-size: 0.95rem;
  color: var(--text-muted);
  font-weight: 300;
  line-height: 1.8;
  margin-bottom: 2rem;
}

.contact-detail {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1rem;
  font-size: 0.925rem;
  color: var(--text-muted);
}

.contact-detail a {
  color: var(--text);
  font-weight: 400;
}

.contact-detail a:hover {
  color: var(--gold);
}

.contact-form {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.form-group {
  position: relative;
}

.form-group input,
.form-group textarea,
.form-group select {
  width: 100%;
  padding: 0.85rem 0;
  font-family: var(--font-body);
  font-size: 0.95rem;
  font-weight: 300;
  color: var(--text);
  background: transparent;
  border: none;
  border-bottom: 1px solid var(--border);
  outline: none;
  transition: border-color var(--transition);
  resize: vertical;
}

.form-group input::placeholder,
.form-group textarea::placeholder {
  color: var(--text-muted);
  opacity: 0.6;
}

.form-group input:focus,
.form-group textarea:focus,
.form-group select:focus {
  border-bottom-color: var(--gold);
}

.form-group textarea {
  min-height: 100px;
}

.form-group select {
  -webkit-appearance: none;
  appearance: none;
  background: transparent;
  cursor: pointer;
  color: var(--text-muted);
}

.form-group select option {
  background: var(--surface);
  color: var(--text);
}

.form-group select:focus,
.form-group select:valid {
  color: var(--text);
}

.btn-submit {
  align-self: flex-start;
  padding: 0.85rem 2.5rem;
  font-family: var(--font-body);
  font-size: 0.8rem;
  font-weight: 400;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--bg);
  background: var(--gold);
  border: 1px solid var(--gold);
  cursor: pointer;
  transition: background var(--transition), color var(--transition);
}

.btn-submit:hover,
.btn-submit:focus-visible {
  background: transparent;
  color: var(--gold);
}

.form-feedback {
  font-size: 0.85rem;
  font-weight: 300;
  margin-top: 0.25rem;
}

.form-feedback.success {
  color: var(--gold);
}

.form-feedback.error {
  color: #c96e6e;
}

/* ============================================================
   Footer
   ============================================================ */
.footer {
  background: var(--footer-bg);
  padding: 4rem 1.5rem 2rem;
  border-top: 1px solid rgba(255, 255, 255, 0.04);
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr;
  gap: 3rem;
  max-width: var(--max-width);
  margin: 0 auto 3rem;
}

.footer-brand .nav-logo {
  font-size: 1.25rem;
  margin-bottom: 0.75rem;
}

.footer-tagline {
  font-size: 0.875rem;
  color: var(--text-muted);
  font-weight: 300;
  line-height: 1.7;
}

.footer-col h4 {
  font-family: var(--font-body);
  font-size: 0.75rem;
  font-weight: 400;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--gold);
  margin-bottom: 1.25rem;
}

.footer-links {
  list-style: none;
}

.footer-links li {
  margin-bottom: 0.65rem;
}

.footer-links a {
  font-size: 0.875rem;
  color: var(--text-muted);
  font-weight: 300;
  text-decoration: none;
  transition: color var(--transition);
}

.footer-links a:hover {
  color: var(--gold);
}

.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: var(--max-width);
  margin: 0 auto;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
  flex-wrap: wrap;
  gap: 1rem;
}

.footer-copyright {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 300;
}

.footer-legal {
  display: flex;
  gap: 1.5rem;
  list-style: none;
}

.footer-legal a {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-weight: 300;
}

.footer-legal a:hover {
  color: var(--gold);
}

/* ============================================================
   Legal Pages (Privacy / Terms)
   ============================================================ */
.legal-page {
  padding: 8rem 1.5rem 5rem;
  background: var(--bg);
  min-height: 100vh;
}

.legal-container {
  max-width: 760px;
  margin: 0 auto;
}

.legal-container h1 {
  font-family: var(--font-heading);
  font-size: clamp(2rem, 4vw, 3rem);
  font-weight: 500;
  color: var(--text);
  margin-bottom: 0.75rem;
}

.legal-container .legal-date {
  font-size: 0.85rem;
  color: var(--text-muted);
  font-weight: 300;
  margin-bottom: 2.5rem;
  display: block;
}

.legal-divider {
  height: 1px;
  background: var(--gold);
  opacity: 0.3;
  margin-bottom: 2.5rem;
}

.legal-body h2 {
  font-family: var(--font-heading);
  font-size: 1.45rem;
  font-weight: 500;
  color: var(--text);
  margin-top: 2.5rem;
  margin-bottom: 0.85rem;
}

.legal-body h2:first-child {
  margin-top: 0;
}

.legal-body h3 {
  font-family: var(--font-body);
  font-size: 0.8rem;
  font-weight: 400;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--gold);
  margin-top: 2rem;
  margin-bottom: 0.5rem;
}

.legal-body p {
  font-size: 0.95rem;
  font-weight: 300;
  color: var(--text-muted);
  line-height: 1.9;
  margin-bottom: 1.25rem;
}

.legal-body ul,
.legal-body ol {
  margin-bottom: 1.5rem;
  padding-left: 1.5rem;
}

.legal-body li {
  font-size: 0.95rem;
  font-weight: 300;
  color: var(--text-muted);
  line-height: 1.9;
  margin-bottom: 0.5rem;
}

.legal-body strong {
  font-weight: 400;
  color: var(--text);
}

.legal-body a {
  color: var(--gold);
}

.legal-back {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: 3rem;
  font-weight: 300;
  transition: color var(--transition);
  text-decoration: none;
}

.legal-back:hover {
  color: var(--gold);
}

.legal-back svg {
  width: 16px;
  height: 16px;
  transition: transform var(--transition);
}

.legal-back:hover svg {
  transform: translateX(-3px);
}

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 900px) {
  .expertise-grid {
    grid-template-columns: 1fr;
    gap: 2rem;
  }

  .contact-grid {
    grid-template-columns: 1fr;
    gap: 3rem;
  }

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

@media (max-width: 768px) {
  .nav-links {
    position: fixed;
    top: 0;
    right: -100%;
    width: 280px;
    height: 100vh;
    background: var(--surface);
    flex-direction: column;
    justify-content: center;
    align-items: flex-start;
    padding: 4rem 2.5rem;
    gap: 1.75rem;
    transition: right var(--transition);
    border-left: 1px solid var(--border);
    z-index: 1000;
  }

  .nav-links.active {
    right: 0;
  }

  .nav-links a {
    font-size: 0.875rem;
  }

  .hamburger {
    display: flex;
  }

  .metrics-grid {
    gap: 2rem;
  }

  .metric-value {
    font-size: 2.3rem;
  }

  .hero-title {
    font-size: clamp(2.2rem, 10vw, 3.5rem);
  }

  .process-list::before {
    left: 4px;
  }

  .footer-bottom {
    flex-direction: column;
    align-items: flex-start;
  }
}

@media (max-width: 480px) {
  .section {
    padding: 4.5rem 1.5rem;
  }

  .services-grid {
    grid-template-columns: 1fr;
  }

  .metrics-grid {
    flex-direction: column;
    gap: 1.5rem;
  }

  .metric-dot {
    width: 0;
    height: 0;
    display: none;
  }

  .hero-underline {
    width: 40px;
  }
}

/* Focus visible */
:focus-visible {
  outline: 1px solid var(--gold);
  outline-offset: 2px;
}

/* Selection */
::selection {
  background: rgba(201, 169, 110, 0.25);
  color: var(--text);
}