/* EduLearnGraph 营销页 — mobile-first，无框架 */
:root {
  --brand: #2970ff;
  --brand-dark: #1d54c4;
  --ink: #1a2233;
  --ink-soft: #47506a;
  --bg: #ffffff;
  --bg-soft: #f4f7fc;
  --border: #e3e9f4;
  --radius: 16px;
  --shadow: 0 10px 30px rgba(26, 34, 51, 0.08);
  --maxw: 1200px;
  font-size: 16px;
}

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

html {
  scroll-behavior: smooth;
}

body {
  font-family:
    'PingFang SC',
    'Microsoft YaHei',
    'Noto Sans SC',
    system-ui,
    -apple-system,
    sans-serif;
  color: var(--ink);
  background: var(--bg);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

img,
video {
  max-width: 100%;
  display: block;
}

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

/* ---------- 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 0 24px;
  border-radius: 999px;
  font-size: 1rem;
  font-weight: 600;
  border: 1.5px solid transparent;
  cursor: pointer;
  transition:
    background 0.2s,
    color 0.2s,
    border-color 0.2s,
    transform 0.15s;
}
.btn:active {
  transform: scale(0.97);
}

.btn--primary {
  background: var(--brand);
  color: #fff;
}
.btn--primary:hover {
  background: var(--brand-dark);
}

.btn--ghost {
  color: var(--ink);
}
.btn--ghost:hover {
  background: var(--bg-soft);
}

.btn--outline {
  border-color: var(--brand);
  color: var(--brand);
  background: #fff;
}
.btn--outline:hover {
  background: #eef4ff;
}

.btn--lg {
  min-height: 54px;
  padding: 0 32px;
  font-size: 1.05rem;
}
.btn--xl {
  min-height: 58px;
  padding: 0 40px;
  font-size: 1.15rem;
}

/* ---------- 导航 ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 20px;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}
.nav__logo {
  display: flex;
  align-items: center;
  gap: 8px;
  font-weight: 700;
  font-size: 1.1rem;
  letter-spacing: 0.2px;
}
.nav__actions {
  display: flex;
  gap: 10px;
}

/* ---------- Hero（第一屏） ---------- */
.hero {
  min-height: 100vh;
  min-height: 100dvh;
  display: flex;
  align-items: center;
  background:
    radial-gradient(900px 480px at 85% -10%, #e8f0ff 0%, transparent 60%),
    radial-gradient(700px 420px at -10% 110%, #f0f6ff 0%, transparent 55%), var(--bg);
  padding: 40px 20px 56px;
}
.hero__inner {
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
}
.hero__copy {
  text-align: center;
}
.hero__copy h1 {
  font-size: clamp(1.75rem, 6vw, 3.4rem);
  line-height: 1.25;
  font-weight: 800;
  letter-spacing: 0.5px;
}
.hero__sub {
  margin-top: 18px;
  font-size: clamp(1rem, 2.6vw, 1.2rem);
  color: var(--ink-soft);
}
.br-pc {
  display: none;
}
.hero__ctas {
  margin-top: 28px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}
.hero__ctas .btn {
  width: 100%;
}

.hero__demos {
  margin-top: 40px;
  display: grid;
  gap: 20px;
}
.demo-card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.demo-card__stage {
  width: 100%;
  aspect-ratio: 16 / 10;
  overflow: hidden;
}
.demo-card__stage iframe {
  width: 100%;
  height: 100%;
  border: 0;
  display: block;
}
.demo-card__cover {
  position: relative;
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  background-size: cover;
  background-position: center;
  transition: transform 0.25s;
}
.demo-card__cover::after {
  /* 半透明遮罩保证按钮可读 */
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, rgba(13, 18, 32, 0.05) 30%, rgba(13, 18, 32, 0.55) 100%);
}
.demo-card__cover:hover {
  transform: scale(1.02);
}
.demo-card__cover--physics {
  background-image: url('/media/physics-demo.jpg');
}
.demo-card__cover--primary {
  background-image: url('/media/primary-math-demo.jpg');
}
.demo-card__cover--math {
  background-image: url('/assets/math-cover.svg');
}
.demo-card__tag {
  position: absolute;
  top: 12px;
  left: 12px;
  z-index: 2;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(13, 18, 32, 0.72);
  color: #fff;
  font-size: 0.78rem;
  letter-spacing: 1px;
}
.demo-card__play {
  position: relative;
  z-index: 2;
  padding: 12px 30px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.95);
  color: #1a2233;
  font-weight: 700;
  font-size: 1rem;
  box-shadow: 0 8px 26px rgba(0, 0, 0, 0.35);
  transition:
    background 0.2s,
    transform 0.2s;
}
.demo-card__cover:hover .demo-card__play {
  background: #fff;
  transform: translateY(-2px);
}
.demo-card {
  display: flex;
  flex-direction: column;
}
.demo-card figcaption {
  flex: 1;
  padding: 14px 18px;
  display: flex;
  flex-direction: column;
  gap: 2px;
  text-align: left;
}
.demo-card figcaption strong {
  font-size: 1.02rem;
}
.demo-card figcaption span {
  font-size: 0.88rem;
  color: var(--ink-soft);
}

/* ---------- 课件弹层（占屏 80%） ---------- */
.demo-modal {
  position: fixed;
  inset: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
}
.demo-modal__mask {
  position: absolute;
  inset: 0;
  background: rgba(10, 15, 28, 0.62);
}
.demo-modal__box {
  position: relative;
  width: min(80vw, 1280px);
  height: 80vh;
  height: 80dvh;
  background: #fff;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 24px 80px rgba(0, 0, 0, 0.4);
}
.demo-modal__box iframe {
  width: 100%;
  height: 100%;
  border: 0;
  display: block;
}
.demo-modal__close {
  position: absolute;
  top: 10px;
  right: 10px;
  z-index: 2;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 0;
  background: rgba(13, 18, 32, 0.6);
  color: #fff;
  font-size: 16px;
  cursor: pointer;
  transition: background 0.2s;
}
.demo-modal__close:hover {
  background: rgba(13, 18, 32, 0.85);
}

/* ---------- 第二屏 ---------- */
.values {
  background: var(--bg-soft);
  padding: 72px 20px;
}
.section-inner {
  max-width: var(--maxw);
  margin: 0 auto;
}
.section-title {
  text-align: center;
  font-size: clamp(1.4rem, 4vw, 2.1rem);
  font-weight: 800;
  margin-bottom: 36px;
}
.values__grid {
  display: grid;
  gap: 16px;
}
.value-card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 26px 22px;
  box-shadow: var(--shadow);
}
.value-card__icon {
  font-size: 2rem;
  margin-bottom: 10px;
}
.value-card h3 {
  font-size: 1.15rem;
  margin-bottom: 8px;
}
.value-card p {
  color: var(--ink-soft);
  font-size: 0.95rem;
}

.trust {
  margin-top: 40px;
  display: grid;
  gap: 16px;
}
.trust__quote {
  background: #fff;
  border-left: 4px solid var(--brand);
  border-radius: 12px;
  padding: 18px 20px;
  box-shadow: var(--shadow);
}
.trust__quote p {
  font-size: 0.98rem;
}
.trust__quote cite {
  display: block;
  margin-top: 8px;
  font-style: normal;
  color: var(--ink-soft);
  font-size: 0.85rem;
}

.convert {
  margin-top: 48px;
  text-align: center;
  background: linear-gradient(135deg, #e9f1ff, #f6faff);
  border: 1px solid #d4e3ff;
  border-radius: 24px;
  padding: 44px 22px;
}
.convert h2 {
  font-size: clamp(1.35rem, 4vw, 1.9rem);
  font-weight: 800;
}
.convert > p {
  margin-top: 10px;
  color: var(--ink-soft);
}
.convert__actions {
  margin-top: 26px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 18px;
}
.convert__actions .btn {
  width: 100%;
}
.convert__qr {
  border-radius: 10px;
  border: 1px solid var(--border);
  background: #fff;
  padding: 8px;
}

/* ---------- 页脚 ---------- */
.footer {
  border-top: 1px solid var(--border);
  padding: 22px 20px;
}
.footer__inner {
  max-width: var(--maxw);
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  color: var(--ink-soft);
  font-size: 0.85rem;
  text-align: center;
}

/* ---------- Pad ≥768 ---------- */
@media (min-width: 768px) {
  .hero {
    padding: 56px 32px;
  }
  .hero__ctas {
    flex-direction: row;
    justify-content: center;
  }
  .hero__ctas .btn {
    width: auto;
  }
  .hero__demos {
    grid-template-columns: 1fr 1fr;
    align-items: stretch;
  }
  .hero__demos .demo-card:first-child {
    grid-column: span 2;
  }
  .values__grid {
    grid-template-columns: repeat(3, 1fr);
  }
  .trust {
    grid-template-columns: 1fr 1fr;
  }
  .convert__actions {
    flex-direction: row;
    justify-content: center;
  }
  .convert__actions .btn {
    width: auto;
  }
  .footer__inner {
    flex-direction: row;
    justify-content: space-between;
  }
}

/* ---------- PC ≥1200 ---------- */
@media (min-width: 1200px) {
  .hero__inner {
    display: grid;
    grid-template-columns: minmax(480px, 1fr) minmax(520px, 1.1fr);
    align-items: center;
    gap: 48px;
  }
  .hero__copy {
    text-align: left;
  }
  .hero__ctas {
    justify-content: flex-start;
  }
  .br-pc {
    display: inline;
  }
  .demo-card__media {
    max-height: 480px;
  }
}