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

:root {
  --primary: #D94B3B;
  --primary-dark: #B83A2D;
  --dark: #2C3E50;
  --gray: #F8F9FA;
  --text: #333;
  --text-light: #666;
  --white: #fff;
  --shadow: 0 2px 12px rgba(0,0,0,0.08);
  --shadow-lg: 0 8px 30px rgba(0,0,0,0.12);
  --radius: 12px;
  --font: -apple-system, "PingFang SC", "Microsoft YaHei", "Helvetica Neue", sans-serif;
}

html { scroll-behavior: smooth; scroll-padding-top: 80px; }
body { font-family: var(--font); color: var(--text); line-height: 1.6; }

.container { max-width: 1100px; margin: 0 auto; padding: 0 24px; }

/* === Header === */
.header {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  background: var(--white); transition: box-shadow 0.3s;
}
.header--scrolled { box-shadow: var(--shadow); }

.nav {
  display: flex; align-items: center; justify-content: space-between;
  height: 64px;
}
.nav__logo {
  font-size: 1.25rem; font-weight: 700; color: var(--primary);
  text-decoration: none;
}
.nav__list { display: flex; list-style: none; gap: 24px; align-items: center; }
.nav__link {
  text-decoration: none; color: var(--text); font-size: 0.95rem;
  transition: color 0.2s; padding: 4px 0;
  border-bottom: 2px solid transparent;
}
.nav__link:hover, .nav__link--active { color: var(--primary); border-bottom-color: var(--primary); }
.nav__link--cta {
  background: var(--primary); color: var(--white) !important;
  padding: 8px 20px; border-radius: 6px; border-bottom: none !important;
}
.nav__link--cta:hover { background: var(--primary-dark); }

/* === Hero === */
.hero {
  padding: 140px 0 80px; text-align: center;
  background: linear-gradient(135deg, var(--dark) 0%, #1a252f 100%);
  color: var(--white);
}
.hero__title { font-size: 2.8rem; font-weight: 800; margin-bottom: 16px; }
.hero__subtitle { font-size: 1.2rem; opacity: 0.85; margin-bottom: 36px; max-width: 500px; margin-left: auto; margin-right: auto; }

/* === Buttons === */
.btn {
  display: inline-block; text-decoration: none; font-weight: 600;
  border-radius: 8px; transition: all 0.2s; cursor: pointer; border: none;
}
.btn--primary { background: var(--primary); color: var(--white); }
.btn--primary:hover { background: var(--primary-dark); transform: translateY(-2px); box-shadow: var(--shadow-lg); }
.btn--lg { padding: 14px 36px; font-size: 1.1rem; }

/* === Sections === */
.section { padding: 80px 0; }
.section--alt { background: var(--gray); }
.section--dark { background: var(--dark); color: var(--white); }
.section__title { font-size: 2rem; font-weight: 700; text-align: center; margin-bottom: 12px; }
.section__title--light { color: var(--white); }
.section__desc { text-align: center; color: var(--text-light); margin-bottom: 48px; font-size: 1.05rem; }

/* === Feature Cards === */
.features-grid {
  display: grid; grid-template-columns: repeat(4, 1fr);
  gap: 24px;
}
.card {
  background: var(--white); border-radius: var(--radius); padding: 32px 24px;
  text-align: center; transition: transform 0.3s, box-shadow 0.3s;
  box-shadow: var(--shadow);
}
.card:hover { transform: translateY(-6px); box-shadow: var(--shadow-lg); }
.card__icon { font-size: 2.5rem; display: block; margin-bottom: 16px; }
.card__title { font-size: 1.1rem; font-weight: 600; margin-bottom: 8px; }
.card__desc { font-size: 0.9rem; color: var(--text-light); line-height: 1.5; }

/* === Highlights === */
.highlights { display: grid; grid-template-columns: repeat(3, 1fr); gap: 32px; }
.highlight { text-align: center; padding: 24px; }
.highlight__icon { font-size: 3rem; display: block; margin-bottom: 16px; }
.highlight__title { font-size: 1.2rem; font-weight: 600; margin-bottom: 8px; }
.highlight__desc { color: var(--text-light); font-size: 0.95rem; }

/* === Tech Tags === */
.tech-tags { display: flex; flex-wrap: wrap; justify-content: center; gap: 12px; }
.tag {
  background: var(--white); padding: 10px 20px; border-radius: 20px;
  font-size: 0.9rem; font-weight: 500; box-shadow: var(--shadow);
}

/* === Download === */
.download { text-align: center; }
.download__version { color: rgba(255,255,255,0.7); margin-bottom: 24px; }
.download__note { margin-top: 16px; font-size: 0.85rem; color: rgba(255,255,255,0.5); }

/* === Footer === */
.footer { padding: 24px 0; text-align: center; font-size: 0.85rem; color: var(--text-light); }

/* === Fade-in Animation === */
.fade-in { opacity: 0; transform: translateY(24px); transition: opacity 0.6s, transform 0.6s; }
.fade-in--visible { opacity: 1; transform: translateY(0); }

/* === Responsive === */
@media (max-width: 900px) {
  .features-grid { grid-template-columns: repeat(2, 1fr); }
  .hero__title { font-size: 2.2rem; }
}
@media (max-width: 600px) {
  .features-grid { grid-template-columns: 1fr; }
  .highlights { grid-template-columns: 1fr; }
  .hero { padding: 120px 0 60px; }
  .hero__title { font-size: 1.8rem; }
  .hero__subtitle { font-size: 1rem; }
  .section { padding: 60px 0; }
  .nav__list { gap: 16px; }
  .nav__link--cta { padding: 6px 14px; font-size: 0.85rem; }
}