/* ─── BMW M Design Tokens ─────────────────────────────── */
:root {
  --canvas: #000000;
  --surface-soft: #0d0d0d;
  --surface-card: #1a1a1a;
  --surface-elevated: #262626;
  --ink: #ffffff;
  --body: #bbbbbb;
  --body-strong: #e6e6e6;
  --muted: #7e7e7e;
  --hairline: #3c3c3c;
  --hairline-strong: #262626;
  --m-blue-light: #0066b1;
  --m-blue-dark: #1c69d4;
  --m-red: #e22718;
  --accent: #ea672b;
  --sp-xxs: 4px; --sp-xs: 8px; --sp-sm: 12px; --sp-md: 16px;
  --sp-lg: 24px; --sp-xl: 40px; --sp-xxl: 64px; --sp-section: 96px;
}

/* ─── Reset & Base ────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--canvas);
  color: var(--ink);
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}

/* ─── NAVBAR (homepage-style) ───────────────────────────── */
.nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  display: flex; align-items: center; justify-content: space-between;
  gap: 24px;
  padding: 16px 24px;
  background: rgba(8, 8, 8, 0.88);
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
  backdrop-filter: blur(18px) saturate(150%);
  -webkit-backdrop-filter: blur(18px) saturate(150%);
}
.nav a { text-decoration: none; }
.nav-logo {
  display: inline-flex; align-items: center; gap: 12px;
  min-height: 44px; color: #fff; text-decoration: none;
  transition: opacity 0.2s;
}
.nav-logo:hover { opacity: 0.72; }
.nav-logo:focus-visible,
.nav-links a:focus-visible,
.nav-toggle:focus-visible,
.nav-overlay-links a:focus-visible {
  outline: 2px solid #1ed760;
  outline-offset: 4px;
  border-radius: 8px;
  opacity: 1;
}
.nav-mark { width: 32px; height: 32px; flex-shrink: 0; display: block; }
.nav-copy { display: flex; flex-direction: column; gap: 2px; min-width: 0; }
.nav-title {
  font-size: 14px; font-weight: 700; line-height: 1.1; letter-spacing: 0.02em;
  color: #fdfdfd; white-space: nowrap;
}
.nav-subtitle {
  font-size: 9px; font-weight: 600; line-height: 1.2; letter-spacing: 0.18em;
  text-transform: uppercase; color: #7c7c7c; white-space: nowrap;
}
.nav-links { display: flex; align-items: center; gap: 40px; }
.nav-links a {
  position: relative; color: #b3b3b3;
  font-size: 14px; font-family: 'PingFang SC', 'Noto Sans SC', sans-serif;
  font-weight: 400; line-height: 1.5; padding-bottom: 4px;
  transition: color 0.2s;
}
.nav-links a:hover,
.nav-links a.is-active,
.nav-links a[aria-current="page"] { color: #fdfdfd; }
.nav-links a.is-active::after,
.nav-links a[aria-current="page"]::after {
  content: ''; position: absolute; left: 0; bottom: 0; width: 100%; height: 2px;
  border-radius: 999px; background: #1ed760;
}
.nav-toggle {
  display: none; flex-direction: column; width: 40px; height: 40px; align-items: center; justify-content: center;
  gap: 4px; border: 0; border-radius: 10px; background: rgba(255, 255, 255, 0.06);
  cursor: pointer; padding: 0;
}
.nav-toggle span {
  display: block; width: 18px; height: 2px; background: #fdfdfd;
  transform-origin: center; transition: transform 0.3s ease, opacity 0.3s ease;
}
.nav-toggle.open .b1 { transform: translateY(6px) rotate(45deg); }
.nav-toggle.open .b2 { opacity: 0; transform: scaleX(0); }
.nav-toggle.open .b3 { transform: translateY(-6px) rotate(-45deg); }
.nav-overlay {
  position: fixed; inset: 0; z-index: 99;
  display: flex; align-items: center; justify-content: center;
  background: #000;
  opacity: 0; pointer-events: none;
  transition: opacity 0.35s cubic-bezier(0.23, 1, 0.32, 1);
}
.nav-overlay.open { opacity: 1; pointer-events: auto; }
.nav-overlay-links { display: flex; flex-direction: column; align-items: center; gap: 32px; }
.nav-overlay-links a {
  color: #fdfdfd; font-size: 32px; font-family: 'PingFang SC', 'Noto Sans SC', sans-serif;
  font-weight: 400; transition: opacity 0.2s;
}
.nav-overlay-links a:hover { opacity: 0.5; }
@media (max-width: 767px) {
  .nav-links { display: none; }
  .nav-toggle { display: flex; }
}
@media (min-width: 768px) {
  .nav { padding: 24px 48px; }
}
@media (min-width: 1280px) {
  .nav { padding: 24px 160px; }
}

/* ─── M-Stripe ────────────────────────────────────────── */
.m-stripe {
  height: 4px;
  background: linear-gradient(to right, var(--m-blue-light) 33.3%, var(--m-blue-dark) 66.6%, var(--m-red) 100%);
  flex-shrink: 0;
}

/* ─── Layout ──────────────────────────────────────────── */
.container { max-width: 1440px; margin: 0 auto; padding: 0 160px; }
@media (max-width: 1200px) { .container { padding: 0 80px; } }
@media (max-width: 768px)  { .container { padding: 0 24px; } }

section { min-height: 100vh; }
.section-inner { padding: var(--sp-section) 0; }

/* ─── Typography ──────────────────────────────────────── */
.label {
  font-size: 12px; font-weight: 700; letter-spacing: 2px;
  text-transform: uppercase; color: var(--muted);
  margin-bottom: var(--sp-md);
}
.section-num {
  font-size: 80px; font-weight: 700; line-height: 1;
  color: var(--surface-elevated);
  position: absolute; top: -20px; left: -20px;
  pointer-events: none; user-select: none;
  font-variant-numeric: tabular-nums;
}
.section-title {
  font-size: 48px; font-weight: 700; line-height: 1;
  color: var(--ink); margin-bottom: var(--sp-lg);
}
.section-lead {
  font-size: 20px; font-weight: 300; color: var(--body);
  line-height: 1.7; max-width: 860px;
}
.accent-title { color: var(--accent); }
.muted-text { color: var(--muted); }
.body-text { font-size: 16px; font-weight: 300; color: var(--body); line-height: 1.8; }
.strong-text { font-size: 16px; font-weight: 500; color: var(--body-strong); line-height: 1.8; }

/* ─── Dividers ────────────────────────────────────────── */
.hairline { height: 1px; background: var(--hairline); }
.gap-xl { height: var(--sp-xl); }
.gap-xxl { height: var(--sp-xxl); }
.gap-section { height: var(--sp-section); }

/* ─── Cards ───────────────────────────────────────────── */
.card {
  background: var(--surface-card);
  padding: var(--sp-xl);
}
.card-elevated { background: var(--surface-elevated); padding: var(--sp-xl); }
.card-dark { background: var(--canvas); border: 1px solid var(--hairline); padding: var(--sp-xl); }
.card-highlight { background: var(--ink); color: var(--canvas); padding: var(--sp-xl); }
.card-black-text { background: var(--canvas); padding: var(--sp-xl); }

/* ─── Grids ───────────────────────────────────────────── */
.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: var(--sp-lg); }
.grid-3 { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: var(--sp-lg); }
.grid-4 { display: grid; grid-template-columns: 1fr 1fr 1fr 1fr; gap: var(--sp-xl); }
.grid-5 { display: grid; grid-template-columns: repeat(5, 1fr); gap: var(--sp-lg); }
@media (max-width: 1100px) { .grid-4 { grid-template-columns: 1fr 1fr; } .grid-5 { grid-template-columns: 1fr 1fr; } }
@media (max-width: 900px)  { .grid-3 { grid-template-columns: 1fr 1fr; } }
@media (max-width: 640px)  { .grid-2, .grid-3, .grid-4, .grid-5 { grid-template-columns: 1fr; } }

/* ─── Buttons ─────────────────────────────────────────── */
.btn {
  display: inline-block; padding: 14px 32px; height: 48px;
  font-size: 12px; font-weight: 700; letter-spacing: 2px;
  text-transform: uppercase; text-decoration: none;
  border: 1px solid var(--ink); color: var(--ink);
  background: transparent; cursor: pointer;
  transition: background 0.2s, color 0.2s;
}
.btn:hover { background: var(--ink); color: var(--canvas); }

/* ─── Reveal Animations ───────────────────────────────── */
.reveal {
  opacity: 0; transform: translateY(28px);
  transition: opacity 0.75s cubic-bezier(0.25,0.46,0.45,0.94),
              transform 0.75s cubic-bezier(0.25,0.46,0.45,0.94);
}
.reveal.visible { opacity: 1; transform: translateY(0); }
.reveal-delay-1 { transition-delay: 0.1s; }
.reveal-delay-2 { transition-delay: 0.2s; }
.reveal-delay-3 { transition-delay: 0.3s; }
.reveal-delay-4 { transition-delay: 0.4s; }

/* ─── SECTION 1: Hero ─────────────────────────────────── */
#hero {
  position: relative;
  min-height: 100vh;
  background: #000;
  display: flex; flex-direction: column; justify-content: flex-end;
  overflow: hidden;
}
.hero-bg {
  position: absolute; inset: 0;
  background: radial-gradient(ellipse 120% 80% at 75% 50%,
    rgba(60,84,167,0.35) 0%, rgba(11,21,41,0.8) 55%, #000 100%);
}
.hero-noise {
  position: absolute; inset: 0; opacity: 0.03;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}
.hero-tv-area {
  position: absolute; right: 160px; top: 208px;
  width: clamp(400px, 52vw, 820px);
}
.hero-img-frame {
  background: #0a0a0a;
  border: 8px solid #111;
  border-radius: 6px;
  line-height: 0;
  box-shadow:
    inset 0 0 0 1px rgba(255,255,255,0.06),
    0 8px 32px rgba(0,0,0,0.5),
    0 24px 72px rgba(0,0,0,0.6),
    0 48px 120px rgba(0,0,0,0.4);
}
.hero-img-frame img {
  width: 100%; height: auto; display: block;
  border-radius: 1px;
}
.tv-frame {
  position: relative; width: 100%; aspect-ratio: 16/9;
  box-shadow:
    0 4px 12px rgba(0,0,0,0.12), 0 8px 28px rgba(0,0,0,0.18),
    0 16px 52px rgba(0,0,0,0.22), 0 32px 96px rgba(0,0,0,0.28),
    0 64px 180px rgba(0,0,0,0.36);
}
.tv-screen {
  width: 100%; height: 100%;
  background: linear-gradient(135deg, #0b1528 0%, #0d2040 40%, #091530 100%);
  display: flex; align-items: center; justify-content: center;
  overflow: hidden; position: relative;
}
.tv-screen-inner {
  width: 92%; height: 88%;
  display: grid;
  grid-template-rows: auto 1fr auto;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 6px;
}
.tv-bar {
  background: rgba(28,105,212,0.15);
  border: 1px solid rgba(28,105,212,0.3);
  border-radius: 1px;
}
.tv-bar-tall { grid-row: span 2; }
.tv-header {
  grid-column: span 3;
  background: rgba(28,105,212,0.1);
  border-bottom: 1px solid rgba(28,105,212,0.2);
  display: flex; align-items: center; padding: 0 8px; gap: 6px;
}
.tv-dot { width: 4px; height: 4px; border-radius: 50%; background: var(--m-blue-dark); }
.tv-dot:nth-child(2) { background: var(--accent); }
.tv-dot:nth-child(3) { background: var(--m-red); }
.tv-chart-bars {
  display: flex; align-items: flex-end; gap: 3px;
  padding: 8px; height: 100%;
}
.tv-chart-bar {
  flex: 1; background: rgba(28,105,212,0.5);
  border-top: 1px solid rgba(28,105,212,0.8);
}
.tv-footer { grid-column: span 3; background: rgba(28,105,212,0.08); }
.hero-content {
  position: relative; z-index: 2;
  padding: 0 160px 120px;
  max-width: 720px;
}
@media (max-width: 1200px) { .hero-content { padding: 0 80px 80px; } .hero-tv-area { right: 80px; width: clamp(320px, 48vw, 700px); } }
@media (max-width: 900px) { .hero-content { padding: 0 48px 60px; } .hero-tv-area { right: 48px; width: clamp(280px, 44vw, 600px); } }
@media (max-width: 768px) { .hero-content { padding: 0 24px 60px; max-width: 100%; } .hero-tv-area { display: none; } }
.hero-eyebrow { font-size: 12px; font-weight: 700; letter-spacing: 3px; color: var(--accent); text-transform: uppercase; margin-bottom: var(--sp-md); }
.hero-title { font-size: clamp(40px, 5vw, 64px); font-weight: 700; line-height: 1; margin-bottom: var(--sp-md); }
.hero-divider { width: 64px; height: 1px; background: var(--hairline); margin: var(--sp-lg) 0; }
.hero-desc { font-size: 16px; font-weight: 300; color: var(--body-strong); line-height: 1.8; max-width: 520px; margin-bottom: var(--sp-xl); }
.hero-meta { display: flex; gap: var(--sp-xxl); flex-wrap: wrap; }
.hero-meta-item { display: flex; flex-direction: column; gap: 6px; }
.hero-meta-label { font-size: 11px; font-weight: 700; letter-spacing: 2px; color: var(--muted); text-transform: uppercase; }
.hero-meta-value { font-size: 14px; font-weight: 500; color: var(--body-strong); line-height: 1.5; }
.hero-kpis { display: flex; gap: 0; margin-bottom: var(--sp-xl); }
.hero-kpi {
  padding: 20px 28px; border: 1px solid var(--hairline);
  border-right: none;
}
.hero-kpi:last-child { border-right: 1px solid var(--hairline); }
.hero-kpi-value { font-size: 36px; font-weight: 700; color: var(--accent); line-height: 1; }
.hero-kpi-label { font-size: 11px; font-weight: 400; color: var(--muted); letter-spacing: 0.5px; margin-top: 4px; }
.hero-bottom { height: 4px; background: linear-gradient(to right, var(--m-blue-light) 33.3%, var(--m-blue-dark) 66.6%, var(--m-red) 100%); }

/* ─── SECTION 2: 项目概览 ─────────────────────────────── */
#overview { background: var(--surface-soft); }
.overview-charts { display: grid; grid-template-columns: 280px 1fr 1fr; gap: var(--sp-lg); align-items: stretch; }
.chart-card { display: flex; flex-direction: column; }
@media (max-width: 1100px) { .overview-charts { grid-template-columns: 1fr 1fr; } }
@media (max-width: 640px) { .overview-charts { grid-template-columns: 1fr; } }
.chart-card {
  background: var(--surface-card); padding: var(--sp-lg);
}
.chart-title { font-size: 13px; font-weight: 500; color: var(--body); letter-spacing: 0.3px; margin-bottom: var(--sp-md); }
.overview-bottom {
  background: var(--canvas);
  border-top: 1px solid var(--hairline);
  padding: var(--sp-xxl) 0;
}
.overview-bottom-inner { max-width: 1440px; margin: 0 auto; padding: 0 160px; }
@media (max-width: 1200px) { .overview-bottom-inner { padding: 0 80px; } }
@media (max-width: 768px) { .overview-bottom-inner { padding: 0 24px; } }
.pain-card {
  background: var(--surface-card); padding: var(--sp-lg) var(--sp-xl);
  border-left: 4px solid var(--accent);
}

/* ─── SECTION 3: 难点与挑战 ──────────────────────────── */
#challenge { background: var(--canvas); }
.challenge-quote {
  font-size: clamp(22px, 3vw, 32px); font-weight: 300;
  color: var(--body-strong); line-height: 1.6;
  max-width: 900px; margin: 0 auto;
  text-align: center; padding: 0 40px;
}
.challenge-box {
  background: var(--surface-card);
  border: 1px solid var(--hairline);
  padding: var(--sp-xl) var(--sp-xxl);
  max-width: 900px; margin: 0 auto;
  position: relative;
}
.challenge-box::before {
  content: '';
  position: absolute; left: 0; top: 0; bottom: 0;
  width: 4px;
  background: linear-gradient(to bottom, var(--m-blue-light), var(--m-blue-dark), var(--m-red));
}
.challenge-box-text { font-size: 20px; font-weight: 400; color: var(--body-strong); line-height: 1.8; }

/* ─── SECTION 4: 怎么做到的 ──────────────────────────── */
#howto { background: var(--surface-soft); }
.research-placeholder {
  width: 100%; aspect-ratio: 16/7;
  background: var(--surface-card);
  border: 1px solid var(--hairline);
  display: flex; align-items: center; justify-content: center;
  position: relative; overflow: hidden;
}
.research-placeholder::before {
  content: '';
  position: absolute; inset: 0;
  background: repeating-linear-gradient(
    -45deg,
    transparent, transparent 20px,
    rgba(255,255,255,0.02) 20px, rgba(255,255,255,0.02) 21px
  );
}
.placeholder-label {
  font-size: 12px; font-weight: 700; letter-spacing: 2px;
  color: var(--muted); text-transform: uppercase; text-align: center;
  line-height: 1.6;
}

/* ─── SECTION 5: 探索目标 & 发现 ─────────────────────── */
#research { background: var(--canvas); min-height: unset; }
.research-split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--sp-xl);
  align-items: start;
}
.split-left { background: none; padding: 0; }
.split-right {
  background: var(--surface-card);
  padding: 48px 48px 128px;
  border-radius: 2px;
}
@media (max-width: 1100px) { .research-split { grid-template-columns: 1fr; } }
@media (max-width: 768px) { .split-right { padding: 32px 24px; } }
.interview-list { display: flex; flex-direction: column; gap: var(--sp-xl); margin-top: var(--sp-xl); }
.interview-item { display: flex; gap: var(--sp-lg); }
.interview-num {
  font-size: 28px; font-weight: 700; color: var(--hairline-strong);
  line-height: 1; flex-shrink: 0; padding-top: 4px;
  min-width: 44px;
}
.interview-quote { font-size: 16px; font-weight: 300; color: var(--body); line-height: 1.8; }
.opportunity-box {
  background: var(--ink); color: var(--canvas);
  padding: var(--sp-xl); margin-top: var(--sp-xl);
}
.opportunity-box p { font-size: 18px; font-weight: 500; line-height: 1.7; color: var(--canvas); }

/* ─── SECTION 6: 解决方案 ────────────────────────────── */
#solution {
  background: #000;
  position: relative; overflow: hidden;
  display: flex; flex-direction: column; justify-content: center;
  min-height: 100vh; padding: var(--sp-section) 0;
}
.solution-bg {
  position: absolute; inset: 0;
  background: radial-gradient(ellipse 100% 70% at 60% 50%,
    rgba(60,84,167,0.25) 0%, rgba(11,21,41,0.6) 50%, #000 100%);
  pointer-events: none;
}
.solution-inner { position: relative; z-index: 1; }
.solution-tv { max-width: 860px; margin: var(--sp-xxl) auto 0; }

/* ─── SECTION 7: 视觉呈现原则 ───────────────────────── */
#visual { background: var(--surface-soft); }
.principle-card {
  border-top: 1px solid var(--hairline); padding-top: var(--sp-xl);
}
.principle-title { font-size: 22px; font-weight: 700; color: var(--accent); margin-bottom: var(--sp-md); }
.principle-body { font-size: 15px; font-weight: 300; color: var(--body); line-height: 1.9; }

/* ─── SECTION 8: 交互设计要点 ───────────────────────── */
#interaction { background: var(--canvas); }
.interaction-card {
  background: var(--surface-card);
  padding: var(--sp-xl) var(--sp-lg);
  border-bottom: 3px solid transparent;
  transition: border-color 0.3s;
}
.interaction-card:hover { border-bottom-color: var(--accent); }
.interaction-num { font-size: 40px; font-weight: 700; color: var(--surface-elevated); line-height: 1; margin-bottom: var(--sp-md); }
.interaction-title { font-size: 18px; font-weight: 700; color: var(--ink); margin-bottom: var(--sp-sm); }
.interaction-body { font-size: 14px; font-weight: 300; color: var(--body); line-height: 1.8; }

/* ─── SECTION 9: 设计评估 ────────────────────────────── */
#evaluation {
  background: var(--canvas);
  display: flex; align-items: center; justify-content: center;
  text-align: center;
}
.eval-inner { max-width: 900px; padding: var(--sp-section) 0; }
.eval-text { font-size: 20px; font-weight: 300; color: var(--body); line-height: 1.9; }
.eval-metrics { display: flex; justify-content: center; gap: 0; margin: var(--sp-xxl) 0; }
.eval-metric {
  padding: var(--sp-xl) var(--sp-xxl);
  border: 1px solid var(--hairline); border-right: none;
}
.eval-metric:last-child { border-right: 1px solid var(--hairline); }
.eval-metric-value { font-size: 52px; font-weight: 700; color: var(--ink); line-height: 1; }
.eval-metric-unit { color: var(--accent); }
.eval-metric-label { font-size: 12px; font-weight: 400; color: var(--muted); letter-spacing: 1px; margin-top: 8px; }

/* ─── Footer ──────────────────────────────────────────── */
footer {
  background: var(--surface-soft); border-top: 1px solid var(--hairline);
  padding: var(--sp-xl) 160px;
  display: flex; align-items: center; justify-content: space-between;
}
@media (max-width: 768px) { footer { padding: var(--sp-xl) 24px; flex-direction: column; gap: var(--sp-md); text-align: center; } }
.footer-text { font-size: 12px; color: var(--muted); letter-spacing: 0.5px; }