:root {
  --teal: #0F766E;
  --teal-dark: #115E59;
  --teal-light: #14B8A6;
  --orange: #F59E0B;
  --orange-dark: #D97706;
  --red: #EF4444;
  --text: #111827;
  --text-soft: #4B5563;
  --text-mute: #6B7280;
  --bg: #FAFAF7;
  --card: #FFFFFF;
  --border: #E5E7EB;
  --shadow: 0 1px 3px rgba(0,0,0,0.04), 0 4px 12px rgba(0,0,0,0.04);
  --shadow-lg: 0 4px 8px rgba(0,0,0,0.06), 0 16px 40px rgba(0,0,0,0.08);

  /* 流式排版 —— 最小 16px，最大按视口缩放 */
  --fs-hero: clamp(2rem, 1.4rem + 3vw, 3.5rem);        /* h1 */
  --fs-h2: clamp(1.6rem, 1.2rem + 1.8vw, 2.5rem);      /* section h2 */
  --fs-lede: clamp(1rem, 0.95rem + 0.3vw, 1.125rem);   /* lede */
  --fs-body: 1rem;
  --fs-small: 0.875rem;
  --fs-eyebrow: 0.8125rem;

  --container-pad: clamp(1rem, 0.6rem + 2vw, 1.5rem);
  --section-py: clamp(3rem, 2rem + 4vw, 5rem);
  --gap: clamp(1rem, 0.5rem + 1.5vw, 2.5rem);
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
  font-size: var(--fs-body);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}
img, video { max-width: 100%; display: block; }
a { color: var(--teal); text-decoration: none; }
a:hover { color: var(--teal-dark); }

.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--container-pad);
}

/* === Buttons === */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.18s ease;
  border: 1px solid transparent;
  white-space: nowrap;
  font-size: inherit;
}
.btn-primary {
  background: var(--teal);
  color: #fff;
  box-shadow: 0 2px 6px rgba(15, 118, 110, 0.25);
}
.btn-primary:hover {
  background: var(--teal-dark);
  color: #fff;
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(15, 118, 110, 0.35);
}
.btn-ghost {
  background: transparent;
  color: var(--teal);
  border: 1.5px solid var(--teal);
}
.btn-ghost:hover {
  background: var(--teal);
  color: #fff;
}
.btn-sm { padding: 8px 14px; font-size: 14px; }
.btn-lg { padding: 14px 24px; font-size: 16px; }
.btn-xl { padding: 18px 32px; font-size: clamp(16px, 0.9rem + 0.3vw, 18px); }

/* === Top bar（移动优先） === */
.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(250, 250, 247, 0.92);
  backdrop-filter: saturate(180%) blur(12px);
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.topbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 56px;
  padding: 10px 0;
  gap: 12px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--text);
  font-weight: 700;
  font-size: clamp(15px, 0.9rem + 0.2vw, 18px);
  flex-shrink: 0;
}
.brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  background: var(--teal);
  color: #fff;
  font-size: 16px;
}
.brand-text small {
  font-weight: 400;
  color: var(--text-mute);
  font-size: 12px;
  margin-left: 4px;
}
.nav {
  display: flex;
  align-items: center;
  gap: 16px;
}
.nav a:not(.btn) {
  color: var(--text-soft);
  font-size: 15px;
  white-space: nowrap;
}
.nav a:not(.btn):hover { color: var(--teal); }

/* === Hero（移动优先：单列；大屏变双列） === */
.hero {
  padding: clamp(32px, 1.5rem + 3vw, 60px) 0 clamp(40px, 2rem + 3vw, 80px);
  background: linear-gradient(180deg, #F0FDFA 0%, var(--bg) 100%);
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: '';
  position: absolute;
  top: -100px;
  right: -150px;
  width: clamp(300px, 30vw, 500px);
  height: clamp(300px, 30vw, 500px);
  background: radial-gradient(circle, rgba(245, 158, 11, 0.15) 0%, transparent 70%);
  border-radius: 50%;
  pointer-events: none;
}
.hero-inner {
  display: grid;
  grid-template-columns: 1fr;
  gap: 32px;
  align-items: center;
  position: relative;
}
.eyebrow {
  display: inline-block;
  color: var(--teal);
  font-weight: 600;
  font-size: var(--fs-eyebrow);
  letter-spacing: 0.5px;
  text-transform: uppercase;
  background: rgba(15, 118, 110, 0.08);
  padding: 6px 12px;
  border-radius: 999px;
  margin: 0 0 16px;
}
.hero h1 {
  font-size: var(--fs-hero);
  line-height: 1.1;
  margin: 0 0 20px;
  font-weight: 800;
  letter-spacing: -0.025em;
}
.hero h1 em {
  font-style: normal;
  color: var(--orange);
  position: relative;
  display: inline-block;
}
.hero h1 em::after {
  content: '';
  position: absolute;
  left: 0;
  right: 0;
  bottom: 4px;
  height: 0.18em;
  background: rgba(245, 158, 11, 0.3);
  z-index: -1;
}
.lede {
  font-size: var(--fs-lede);
  color: var(--text-soft);
  margin: 0 0 24px;
  line-height: 1.65;
}
.lede strong {
  color: var(--text);
  font-weight: 600;
  background: linear-gradient(180deg, transparent 60%, rgba(245, 158, 11, 0.25) 60%);
}
.cta {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-bottom: 24px;
}
.trust-strip {
  display: flex;
  gap: clamp(16px, 1rem + 1vw, 28px);
  flex-wrap: wrap;
  padding-top: 20px;
  border-top: 1px solid var(--border);
  font-size: var(--fs-small);
  color: var(--text-soft);
}
.trust-strip strong {
  color: var(--teal);
  font-size: clamp(16px, 0.9rem + 0.3vw, 20px);
  font-weight: 700;
  margin-right: 4px;
}

/* Hero 视频（移动优先） */
.hero-video {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 0;
}
.video-frame {
  width: 100%;
  max-width: min(420px, 100%);
  aspect-ratio: 3/4;
  background: #F3F4F6 url('demos/poster_chin_tuck.png') center/cover no-repeat;
  border-radius: 24px;
  overflow: hidden;
  box-shadow: var(--shadow-lg);
  border: 4px solid #fff;
  position: relative;
}
.video-frame video {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  z-index: 1;
}
.video-caption {
  margin-top: 14px;
  font-size: 13px;
  color: var(--text-mute);
  text-align: center;
}

/* === 通用 section === */
.section {
  padding: var(--section-py) 0;
}
.section-eyebrow {
  color: var(--teal);
  font-weight: 600;
  font-size: var(--fs-eyebrow);
  letter-spacing: 1px;
  text-transform: uppercase;
  margin: 0 0 12px;
}
.section h2 {
  font-size: var(--fs-h2);
  line-height: 1.2;
  margin: 0 0 16px;
  font-weight: 800;
  letter-spacing: -0.015em;
}
.section-lede {
  font-size: var(--fs-lede);
  color: var(--text-soft);
  max-width: 720px;
  margin: 0 0 32px;
}
.section-lede strong { color: var(--text); font-weight: 600; }

/* === 错 vs 对 对比（移动优先） === */
.compare { background: #FFFFFF; }
.compare-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
  margin-top: 16px;
}
.compare-card {
  padding: 24px 22px;
  border-radius: 20px;
  border: 2px solid;
}
.compare-card.bad {
  background: #FEF2F2;
  border-color: #FCA5A5;
}
.compare-card.good {
  background: #ECFDF5;
  border-color: #6EE7B7;
}
.compare-tag {
  display: inline-block;
  font-size: 13px;
  font-weight: 700;
  padding: 4px 10px;
  border-radius: 6px;
  margin-bottom: 14px;
}
.compare-card.bad .compare-tag { background: #FEE2E2; color: #991B1B; }
.compare-card.good .compare-tag { background: #D1FAE5; color: #065F46; }
.compare-card h3 { font-size: 18px; margin: 0 0 14px; font-weight: 700; }
.compare-card ul { list-style: none; padding: 0; margin: 0; }
.compare-card li {
  padding: 6px 0 6px 22px;
  font-size: 15px;
  color: var(--text-soft);
  position: relative;
}
.compare-card li::before {
  position: absolute;
  left: 0;
  font-weight: 700;
}
.compare-card.bad li::before { content: "✗"; color: #DC2626; }
.compare-card.good li::before { content: "✓"; color: #059669; }
.compare-arrow {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 32px;
  color: var(--teal);
  font-weight: 300;
  transform: rotate(90deg);
}

/* === 三步 === */
.how { background: linear-gradient(180deg, #FFFFFF 0%, var(--bg) 100%); }
.steps {
  display: grid;
  grid-template-columns: 1fr;
  gap: 28px;
  margin-top: 32px;
}
.step {
  text-align: left;
  position: relative;
  padding-left: 60px;
}
.step-num {
  position: absolute;
  left: 0;
  top: 0;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--teal) 0%, var(--teal-light) 100%);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 20px;
  box-shadow: 0 4px 10px rgba(15, 118, 110, 0.25);
}
.step h3 { font-size: 20px; margin: 0 0 8px; font-weight: 700; padding-top: 8px; }
.step p { color: var(--text-soft); margin: 0; font-size: 15px; }

/* === 真实视频 demo === */
.demo { background: var(--bg); }
.demo-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 220px), 1fr));
  gap: 20px;
}
.demo-item {
  background: var(--card);
  border-radius: 16px;
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: all 0.2s ease;
  border: 1px solid var(--border);
}
.demo-item:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}
.demo-video {
  aspect-ratio: 3/4;
  background-color: #F3F4F6;
  position: relative;
  overflow: hidden;
}
.demo-item:nth-child(1) .demo-video { background-image: url('demos/poster_chin_tuck.png'); background-size: cover; background-position: center; }
.demo-item:nth-child(2) .demo-video { background-image: url('demos/poster_bridge.png'); background-size: cover; background-position: center; }
.demo-item:nth-child(3) .demo-video { background-image: url('demos/poster_wall_slide.png'); background-size: cover; background-position: center; }
.demo-item:nth-child(4) .demo-video { background-image: url('demos/poster_clamshell.png'); background-size: cover; background-position: center; }
.demo-video video {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
  z-index: 1;
}
.demo-caption {
  padding: 12px 16px;
  display: flex;
  flex-direction: column;
  gap: 2px;
  border-top: 1px solid var(--border);
}
.demo-caption strong { font-size: 15px; color: var(--text); }
.demo-caption span { font-size: 12px; color: var(--red); font-weight: 600; }

/* === 8+14 + 隐私 === */
.inside { background: #FFFFFF; }
.inside-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 32px;
  background: var(--card);
  border-radius: 20px;
  padding: 28px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
  margin-bottom: 28px;
}
.inside-col h3 {
  font-size: 20px;
  font-weight: 700;
  margin: 0 0 20px;
  color: var(--teal-dark);
}
.checklist { list-style: none; padding: 0; margin: 0; }
.checklist li {
  padding: 10px 0 10px 32px;
  border-bottom: 1px solid var(--border);
  position: relative;
  font-size: 15px;
  display: flex;
  align-items: center;
  gap: 10px;
}
.checklist li::before {
  content: "✓";
  position: absolute;
  left: 0;
  color: var(--teal);
  font-weight: 700;
  font-size: 16px;
}
.checklist li:last-child { border-bottom: none; }
.checklist.small li { padding: 8px 0 8px 32px; font-size: 14px; }
.muscle-tag {
  display: inline-block;
  background: rgba(15, 118, 110, 0.1);
  color: var(--teal-dark);
  font-size: 11px;
  padding: 2px 8px;
  border-radius: 4px;
  font-weight: 600;
  min-width: 22px;
  text-align: center;
}

/* === 隐私 === */
.privacy-card {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
  text-align: center;
  background: linear-gradient(135deg, #ECFDF5 0%, #F0FDFA 100%);
  border: 1px solid #A7F3D0;
  border-radius: 16px;
  padding: 24px 20px;
  box-shadow: var(--shadow);
}
.privacy-icon { font-size: 40px; line-height: 1; }
.privacy-body h3 {
  font-size: 20px;
  margin: 0 0 6px;
  color: var(--teal-dark);
  font-weight: 800;
}
.privacy-body p {
  margin: 0;
  font-size: 14px;
  color: var(--text-soft);
  line-height: 1.5;
}
.privacy-body strong { color: var(--teal-dark); }
.privacy-badges {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  justify-content: center;
  gap: 8px;
}
.badge {
  background: #fff;
  border: 1px solid #A7F3D0;
  color: var(--teal-dark);
  padding: 5px 10px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 600;
  white-space: nowrap;
}

/* === FAQ === */
.faq { background: linear-gradient(180deg, #FFFFFF 0%, var(--bg) 100%); }
.faq-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
  max-width: 800px;
  margin: 0 auto;
}
.faq-item {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
  transition: all 0.2s ease;
}
.faq-item[open] {
  border-color: var(--teal);
  box-shadow: 0 2px 8px rgba(15, 118, 110, 0.1);
}
.faq-item summary {
  padding: 18px 20px;
  font-weight: 600;
  font-size: 16px;
  cursor: pointer;
  list-style: none;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  user-select: none;
}
.faq-item summary::-webkit-details-marker { display: none; }
.faq-item summary::after {
  content: "+";
  color: var(--teal);
  font-size: 24px;
  font-weight: 300;
  flex-shrink: 0;
}
.faq-item[open] summary::after { content: "−"; }
.faq-item p {
  padding: 0 20px 18px;
  margin: 0;
  color: var(--text-soft);
  font-size: 15px;
  line-height: 1.7;
}

/* === 下载 === */
.download {
  background: linear-gradient(135deg, var(--teal) 0%, var(--teal-dark) 100%);
  color: #fff;
  text-align: center;
}
.download .section-eyebrow { color: var(--orange); }
.download h2, .download .section-lede { color: #fff; }
.download .section-lede { opacity: 0.9; }
.download-card {
  display: inline-block;
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(10px);
  padding: 32px 28px;
  border-radius: 20px;
  border: 1px solid rgba(255, 255, 255, 0.2);
  margin: 16px 0 40px;
  width: 100%;
  max-width: 480px;
}
.download .btn-primary {
  background: var(--orange);
  box-shadow: 0 4px 12px rgba(245, 158, 11, 0.4);
  width: 100%;
}
.download .btn-primary:hover {
  background: var(--orange-dark);
  box-shadow: 0 6px 20px rgba(245, 158, 11, 0.5);
}
.version { margin: 16px 0 0; font-size: 13px; opacity: 0.7; }

.ios-waitlist {
  max-width: 480px;
  margin: 0 auto;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.2);
  border-radius: 16px;
  padding: 20px;
}
.ios-label {
  font-size: 14px;
  margin: 0 0 12px;
  color: #fff;
  opacity: 0.95;
}
.ios-form { display: flex; gap: 8px; flex-wrap: wrap; }
.ios-form input {
  flex: 1 1 200px;
  min-width: 0;
  padding: 12px 16px;
  border: 1px solid rgba(255, 255, 255, 0.3);
  background: rgba(255, 255, 255, 0.1);
  color: #fff;
  border-radius: 10px;
  font-size: 15px;
  outline: none;
}
.ios-form input::placeholder { color: rgba(255, 255, 255, 0.6); }
.ios-form input:focus { border-color: var(--orange); background: rgba(255, 255, 255, 0.15); }
.ios-form button {
  background: var(--orange);
  color: #fff;
  border: none;
  border-radius: 10px;
  padding: 12px 20px;
  font-weight: 600;
  cursor: pointer;
  font-size: 15px;
  flex: 0 0 auto;
}
.ios-form button:hover { background: var(--orange-dark); }
.ios-msg { margin: 12px 0 0; font-size: 14px; min-height: 20px; }
.ios-msg.success { color: #6EE7B7; }
.ios-msg.error { color: #FCA5A5; }

/* === Footer === */
.footer {
  background: #0F172A;
  color: #94A3B8;
  padding: 28px 0;
  text-align: center;
  font-size: 14px;
}
.footer p { margin: 4px 0; }
.footer .small { font-size: 12px; opacity: 0.7; }

/* === 浮动下载按钮（仅小屏） === */
.float-cta {
  display: inline-flex;
  align-items: center;
  position: fixed;
  bottom: 16px;
  right: 16px;
  z-index: 60;
  background: var(--orange);
  color: #fff;
  padding: 12px 18px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 15px;
  box-shadow: 0 4px 16px rgba(245, 158, 11, 0.45);
  text-decoration: none;
  animation: floatPulse 2.4s ease-in-out infinite;
}
.float-cta:hover { color: #fff; background: var(--orange-dark); }
@keyframes floatPulse {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-4px); }
}

/* === 响应式断点（移动优先，往上加） === */

/* 480px+ 加大屏单列 */
@media (min-width: 480px) {
  .topbar-inner { min-height: 60px; }
  .inside-grid { padding: 32px; }
  .privacy-card { padding: 28px 24px; }
  .download-card { padding: 40px 36px; }
}

/* 640px+ 视频区稍微放大 */
@media (min-width: 640px) {
  .hero-video { max-width: 380px; margin: 0 auto; }
  .compare-card { padding: 28px 26px; }
}

/* 768px+ 切换到双列 + 大字 */
@media (min-width: 768px) {
  .topbar-inner { min-height: 64px; }
  .nav { gap: 24px; }
  .hero-inner {
    grid-template-columns: 1.2fr 1fr;
    gap: 60px;
  }
  .hero-video { max-width: none; }
  .compare-grid {
    grid-template-columns: 1fr auto 1fr;
    gap: 20px;
  }
  .compare-arrow { transform: none; }
  .steps { grid-template-columns: repeat(3, 1fr); gap: 32px; }
  .inside-grid { grid-template-columns: 1fr 1.3fr; gap: 48px; padding: 40px; }
  .privacy-card {
    grid-template-columns: auto 1fr auto;
    text-align: left;
    padding: 28px 32px;
    gap: 24px;
  }
  .privacy-badges { flex-direction: column; }
  .ios-form { flex-wrap: nowrap; }
  .ios-form input { flex: 1 1 auto; }
  .ios-form button { flex: 0 0 auto; }
}

/* 1024px+ 大屏更舒服 */
@media (min-width: 1024px) {
  .nav { gap: 32px; }
  .hero-inner { gap: 80px; }
  .compare-grid { gap: 32px; }
  .inside-grid { padding: 48px; }
  .download-card { padding: 40px 60px; }
  .demo-grid { gap: 24px; }
}

/* 1280px+ 保持居中不拉太宽 */
@media (min-width: 1280px) {
  .container { max-width: 1200px; }
}

/* 大屏（>1024）才隐藏浮动按钮 —— 桌面有完整 nav 不需要它 */
@media (min-width: 1024px) {
  .float-cta { display: none; }
}