/* ========================================
   51标准件 - 主样式表
   专注紧固件知识科普
   ======================================== */

/* ===== Base Reset ===== */
*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { font-family: "Noto Sans SC", -apple-system, "PingFang SC", "Microsoft YaHei", sans-serif; color: #334155; line-height: 1.8; }

/* ===== Container ===== */
.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }

/* ===== Navigation ===== */
.navbar {
  position: fixed; top: 0; left: 0; width: 100%;
  background: transparent;
  z-index: 1000;
  padding: 16px 0;
  transition: all 0.4s ease;
}
.navbar.scrolled {
  background: rgba(17,24,39,0.92);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  padding: 10px 0;
}
.nav-container {
  display: flex; justify-content: flex-end; align-items: center;
}
/* Nav links */
.nav-links { list-style: none; display: flex; gap: 28px; align-items: center; }
.nav-links a {
  color: rgba(255,255,255,0.65); text-decoration: none;
  font-size: 14px; font-weight: 400;
  letter-spacing: 0.5px;
  transition: color 0.2s;
  position: relative;
}
.nav-links a::after {
  content: ''; position: absolute; bottom: -3px; left: 0;
  width: 0; height: 1px; background: #dc2626;
  transition: width 0.3s ease;
}
.nav-links a:hover { color: #ffffff; }
.nav-links a:hover::after { width: 100%; }

/* Hamburger (mobile) */
.hamburger { display: none; flex-direction: column; gap: 5px; cursor: pointer; background: none; border: none; padding: 4px; }
.hamburger span { display: block; width: 22px; height: 2px; background: #fff; border-radius: 2px; transition: 0.3s; }
.hamburger.active span:nth-child(1) { transform: rotate(45deg) translate(5px, 5px); }
.hamburger.active span:nth-child(2) { opacity: 0; }
.hamburger.active span:nth-child(3) { transform: rotate(-45deg) translate(5px, -5px); }

/* Mobile responsive */
@media (max-width: 768px) {
  .hamburger { display: flex; z-index: 1001; }
  .nav-links {
    display: none; flex-direction: column;
    position: fixed; top: 0; right: 0; width: 200px; max-width: 55%; height: 100vh;
    background: rgba(15,43,74,0.98);
    padding: 80px 20px 30px; gap: 14px;
    justify-content: flex-start;
    transform: translateX(100%);
    transition: transform 0.3s ease;
  }
  .nav-links.open {
    display: flex;
    transform: translateX(0);
  }
  .nav-links a { font-size: 16px; }
}

/* ===== Hero Section ===== */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  position: relative;
  overflow: hidden;
}

/* Video background */
.hero-video-wrap {
  position: absolute; inset: 0; z-index: 0;
}
.hero-video {
  width: 100%; height: 100%; object-fit: cover;
}
.hero-overlay {
  position: absolute; inset: 0;
  background: rgba(10,20,35,0.55);
  z-index: 1;
}

.hero-content {
  max-width: 800px;
  position: relative; z-index: 2;
}

/* Badge */
.hero-badge {
  display: inline-block;
  padding: 6px 18px;
  border: 1px solid rgba(255,255,255,0.15);
  border-radius: 20px;
  color: rgba(255,255,255,0.5);
  font-size: 12px; font-weight: 400;
  letter-spacing: 2px;
  margin-bottom: 24px;
}

.hero-title {
  font-size: 4.5rem; font-weight: 700; color: #ffffff;
  margin-bottom: 16px; letter-spacing: 4px;
  text-shadow: 0 2px 30px rgba(0,0,0,0.3);
}

.hero-subtitle {
  font-size: 1.05rem; color: rgba(255,255,255,0.55);
  max-width: 500px; margin: 0 auto;
  line-height: 1.7; letter-spacing: 0.5px;
}

/* Scroll down indicator */
.scroll-down {
  position: absolute; bottom: 36px; left: 50%;
  transform: translateX(-50%); z-index: 2;
  width: 24px; height: 38px;
}
.scroll-down span {
  position: absolute; top: 0; left: 50%;
  width: 20px; height: 34px;
  margin-left: -10px;
  border: 2px solid rgba(255,255,255,0.3);
  border-radius: 10px;
}
.scroll-down span::after {
  content: ''; position: absolute; top: 6px; left: 50%;
  width: 2px; height: 8px;
  margin-left: -1px;
  background: rgba(255,255,255,0.5);
  border-radius: 2px;
  animation: scrollDown 1.5s ease infinite;
}
@keyframes scrollDown {
  0% { opacity: 1; transform: translateY(0); }
  100% { opacity: 0; transform: translateY(12px); }
}

/* Mobile */
@media (max-width: 768px) {
  .hero { min-height: 90vh; }
  .hero-title { font-size: 2.4rem; letter-spacing: 2px; }
  .hero-subtitle { font-size: 0.95rem; padding: 0 20px; }
  .scroll-down { display: none; }
}

/* ===== Section Base ===== */
.section {
  padding: 80px 0;
  opacity: 0;
  transform: translateY(30px);
  transition: all 0.6s ease;
}
.section.visible {
  opacity: 1;
  transform: translateY(0);
}

/* ===== About Section ===== */
.about-section { background: #ffffff; }
.about-grid {
  display: grid; grid-template-columns: 1fr 1fr; gap: 60px; align-items: center;
}
.about-image img {
  width: 100%; border-radius: 12px; box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}
.section-label {
  color: #dc2626; font-size: 14px; font-weight: 700; text-transform: uppercase;
  letter-spacing: 2px; margin-bottom: 8px;
}
.section-title {
  font-size: 2rem; font-weight: 700; color: #111827; margin-bottom: 20px;
}
.about-text p {
  color: #334155; line-height: 1.8; margin-bottom: 16px; font-size: 16px;
}

/* Mobile */
@media (max-width: 768px) {
  .section { padding: 50px 0; }
  .about-grid { grid-template-columns: 1fr; gap: 30px; }
  .section-title { font-size: 1.6rem; }
}

/* ===== Stats Section ===== */
.stats-section {
  background: #f0f4f8;
}
.stats-hint {
  text-align: center; color: #111827; font-size: 2rem;
  font-weight: 700; margin-bottom: 24px;
}
@media (max-width: 768px) {
  .stats-hint { font-size: 1.5rem; margin-bottom: 16px; }
}
.stats-grid {
  display: grid; grid-template-columns: repeat(5, 1fr); gap: 20px;
}
.stat-card {
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  text-align: center; padding: 30px 16px;
  background: #ffffff; border-radius: 12px;
  transition: all 0.3s ease;
  border-bottom: 3px solid transparent;
  text-decoration: none;
  cursor: pointer;
}
.stat-card:hover {
  transform: translateY(-4px);
  border-bottom-color: #dc2626;
  box-shadow: 0 8px 30px rgba(0,0,0,0.08);
}
.stat-number {
  display: block; font-size: 2.5rem; font-weight: 800; color: #dc2626;
  line-height: 1.2; margin-bottom: 8px;
}
.stat-suffix { font-size: 1.2rem; }
.stat-label { display: block; font-size: 15px; color: #64748b; }

/* Mobile */
@media (max-width: 768px) {
  .stats-grid { grid-template-columns: repeat(2, 1fr); gap: 8px; max-width: 360px; margin: 0 auto; }
  .stat-card { padding: 16px 10px; }
  .stat-number { font-size: 1.6rem; }
  .stat-label { font-size: 13px; }
}

/* ===== Platforms Section ===== */
.platforms-section { background: #ffffff; }
.text-center { text-align: center; }
.section-desc {
  color: #64748b; font-size: 16px; margin-bottom: 48px; max-width: 600px; margin-left: auto; margin-right: auto;
}
.platforms-grid {
  display: grid; grid-template-columns: repeat(5, 1fr); gap: 24px;
}
.platform-card {
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  padding: 30px 16px; background: #ffffff;
  border: 1px solid #e2e8f0; border-radius: 12px;
  text-decoration: none; transition: all 0.3s ease;
  text-align: center;
}
.platform-card:hover {
  transform: translateY(-6px); border-color: #dc2626;
  box-shadow: 0 12px 40px rgba(220,38,38,0.1);
}
.platform-icon { width: 100%; display: flex; align-items: center; justify-content: center; }
.platform-icon svg { width: 36px; height: 36px; color: #111827; fill: #111827; display: block; }
/* platform-name removed per user request */
/* platform-action removed */

/* Mobile */
@media (max-width: 992px) {
  .platforms-grid { grid-template-columns: repeat(3, 1fr); }
}
@media (max-width: 768px) {
  .platforms-grid { grid-template-columns: repeat(2, 1fr); gap: 16px; }
  .platform-card { padding: 24px 16px; }
  .section-desc { margin-bottom: 24px; }
}
@media (max-width: 480px) {
  .platforms-grid { grid-template-columns: 1fr; }
}

/* ===== Footer ===== */
.footer {
  background: #111827; padding: 40px 0; text-align: center;
  border-top: 3px solid #dc2626;
}
.footer-tagline { color: #94a3b8; font-size: 15px; margin-bottom: 8px; }
.footer-copyright { color: #64748b; font-size: 13px; }

/* ===== Mobile Fine-tuning ===== */
@media (max-width: 768px) {
  .hero-badge { font-size: 11px; padding: 4px 14px; margin-bottom: 16px; }
  .about-grid { gap: 24px; }
  .about-text p { font-size: 15px; }
  .stats-grid { gap: 12px; }
  .stat-card { padding: 20px 12px; }
  .platforms-grid { gap: 12px; }
  .platform-card { padding: 16px 8px; }
  .platform-icon svg { width: 28px; height: 28px; }
  .platform-name { font-size: 14px; }
}