/* ============================================================
   Suzhou Boyuan Special Transformer Co., Ltd.
   Static site stylesheet — responsive, mobile-first
   ============================================================ */
:root {
  --primary: #0b4f8a;
  --primary-dark: #083a66;
  --accent: #e8a020;
  --text: #2c3138;
  --muted: #5f6b76;
  --bg-light: #f5f7fa;
  --white: #ffffff;
  --border: #e3e8ee;
  --radius: 8px;
  --shadow: 0 2px 12px rgba(11, 45, 79, .08);
  --container: 1180px;
}

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

html { scroll-behavior: smooth; }

body {
  font-family: "Segoe UI", Arial, "Helvetica Neue", sans-serif;
  font-size: 16px;
  line-height: 1.7;
  color: var(--text);
  background: var(--white);
}

img { max-width: 100%; height: auto; display: block; }

a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }

ul { list-style: none; }

.container {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 20px;
}

/* ---------- Top bar ---------- */
.topbar {
  background: var(--primary-dark);
  color: #cddbe8;
  font-size: 13px;
  padding: 6px 0;
}
.topbar .container {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

/* ---------- Header / Nav ---------- */
.site-header {
  background: var(--white);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow);
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: 72px;
  gap: 16px;
}
.logo { display: flex; align-items: center; gap: 10px; }
.logo img { height: 52px; width: auto; }
.logo-text { line-height: 1.25; }
.logo-text strong {
  display: block;
  color: var(--primary-dark);
  font-size: 17px;
}
.logo-text span { font-size: 12px; color: var(--muted); }

.nav-toggle { display: none; }
.nav-toggle-label {
  display: none;
  cursor: pointer;
  padding: 10px;
}
.nav-toggle-label span,
.nav-toggle-label span::before,
.nav-toggle-label span::after {
  display: block;
  background: var(--primary);
  height: 2px;
  width: 26px;
  position: relative;
  transition: .25s ease;
  content: "";
}
.nav-toggle-label span::before { top: -8px; }
.nav-toggle-label span::after { top: 6px; }

.main-nav ul { display: flex; gap: 4px; }
.main-nav a {
  display: block;
  padding: 10px 14px;
  font-weight: 600;
  font-size: 15px;
  color: var(--text);
  border-radius: 6px;
}
.main-nav a:hover,
.main-nav a.active {
  color: var(--white);
  background: var(--primary);
  text-decoration: none;
}
.nav-cta {
  background: var(--accent);
  color: #fff !important;
}
.nav-cta:hover, .nav-cta.active { background: #c9881a !important; }

/* ---------- Hero / banner ---------- */
.hero {
  position: relative;
  background: var(--primary-dark) url("/img/banner.jpg") center/cover no-repeat;
  min-height: 420px;
  display: flex;
  align-items: center;
}
.hero::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(90deg, rgba(5,30,55,.85) 0%, rgba(5,30,55,.55) 55%, rgba(5,30,55,.15) 100%);
}
.hero-content {
  position: relative;
  z-index: 2;
  color: var(--white);
  max-width: 640px;
  padding: 60px 0;
}
.hero-content h1 {
  font-size: 40px;
  line-height: 1.2;
  margin-bottom: 16px;
}
.hero-content p { font-size: 18px; color: #dbe7f2; margin-bottom: 26px; }
.btn {
  display: inline-block;
  padding: 12px 28px;
  border-radius: 6px;
  font-weight: 700;
  font-size: 15px;
  border: none;
  cursor: pointer;
}
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: #c9881a; text-decoration: none; }
.btn-outline { border: 2px solid #fff; color: #fff; margin-left: 12px; }
.btn-outline:hover { background: rgba(255,255,255,.15); text-decoration: none; }

/* ---------- Page banner (inner pages) ---------- */
.page-banner {
  background: var(--primary) linear-gradient(120deg, var(--primary-dark), var(--primary));
  color: #fff;
  padding: 46px 0;
}
.page-banner h1 { font-size: 32px; margin-bottom: 6px; }
.breadcrumb { font-size: 14px; color: #bcd3e6; }
.breadcrumb a { color: #dbe9f5; }

/* ---------- Sections ---------- */
.section { padding: 64px 0; }
.section.alt { background: var(--bg-light); }
.section-title {
  text-align: center;
  font-size: 30px;
  color: var(--primary-dark);
  margin-bottom: 10px;
}
.section-sub {
  text-align: center;
  color: var(--muted);
  max-width: 720px;
  margin: 0 auto 44px;
}

.grid { display: grid; gap: 28px; }
.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(4, 1fr); }

/* ---------- Cards ---------- */
.card {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow);
  transition: transform .2s ease, box-shadow .2s ease;
  display: flex;
  flex-direction: column;
}
.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 22px rgba(11, 45, 79, .15);
}
.card img { width: 100%; aspect-ratio: 4 / 3; object-fit: cover; }
.card-body { padding: 20px; flex: 1; display: flex; flex-direction: column; }
.card-body h3 { color: var(--primary-dark); font-size: 18px; margin-bottom: 8px; }
.card-body h3 a { color: inherit; }
.card-body p { color: var(--muted); font-size: 14.5px; flex: 1; }
.card-link {
  margin-top: 14px;
  font-weight: 700;
  font-size: 14px;
  color: var(--primary);
}

/* ---------- Stats strip ---------- */
.stats { background: var(--primary-dark); color: #fff; padding: 40px 0; }
.stats .grid-4 { gap: 16px; text-align: center; }
.stat-num { font-size: 34px; font-weight: 800; color: var(--accent); }
.stat-label { font-size: 14px; color: #cddbe8; }

/* ---------- Feature list ---------- */
.feature-list li {
  padding-left: 30px;
  position: relative;
  margin-bottom: 12px;
  color: var(--text);
}
.feature-list li::before {
  content: "✓";
  position: absolute;
  left: 0;
  top: 0;
  width: 20px;
  height: 20px;
  background: var(--primary);
  color: #fff;
  border-radius: 50%;
  font-size: 12px;
  line-height: 20px;
  text-align: center;
}

/* ---------- Split layout ---------- */
.split { display: grid; grid-template-columns: 1fr 1fr; gap: 44px; align-items: center; }
.split img { border-radius: var(--radius); box-shadow: var(--shadow); }

/* ---------- Tables ---------- */
.spec-table {
  width: 100%;
  border-collapse: collapse;
  margin: 18px 0;
  font-size: 15px;
}
.spec-table th, .spec-table td {
  border: 1px solid var(--border);
  padding: 10px 14px;
  text-align: left;
}
.spec-table th { background: var(--bg-light); color: var(--primary-dark); width: 34%; }
.spec-table tr:nth-child(even) td { background: #fafbfd; }

/* ---------- Product detail ---------- */
.product-hero { display: grid; grid-template-columns: 1fr 1.1fr; gap: 44px; align-items: start; }
.product-hero img {
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  width: 100%;
}
.product-hero h1 { color: var(--primary-dark); font-size: 32px; margin-bottom: 6px; }
.product-tagline { color: var(--muted); font-size: 17px; margin-bottom: 20px; }
.prose h2 { color: var(--primary-dark); font-size: 24px; margin: 40px 0 14px; padding-bottom: 8px; border-bottom: 2px solid var(--border); }
.prose h3 { color: var(--primary); font-size: 19px; margin: 26px 0 10px; }
.prose p { margin-bottom: 14px; color: var(--text); }
.prose ul { list-style: disc; padding-left: 24px; margin-bottom: 14px; }
.prose ol { padding-left: 26px; margin-bottom: 14px; }
.prose li { margin-bottom: 6px; }

/* ---------- FAQ ---------- */
.faq-item {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 16px;
  overflow: hidden;
}
.faq-item summary {
  cursor: pointer;
  padding: 18px 22px;
  font-weight: 700;
  color: var(--primary-dark);
  font-size: 16.5px;
  list-style: none;
  position: relative;
  padding-right: 46px;
}
.faq-item summary::-webkit-details-marker { display: none; }
.faq-item summary::after {
  content: "+";
  position: absolute;
  right: 20px;
  top: 50%;
  transform: translateY(-50%);
  font-size: 22px;
  color: var(--accent);
}
.faq-item[open] summary::after { content: "–"; }
.faq-item .faq-body { padding: 0 22px 18px; color: var(--text); }
.faq-item .faq-body ul, .faq-item .faq-body ol { padding-left: 24px; margin: 8px 0 14px; }
.faq-item .faq-body li { margin-bottom: 6px; }
.faq-item .faq-body h3 { color: var(--primary); margin: 14px 0 8px; }

/* ---------- CTA band ---------- */
.cta-band {
  background: linear-gradient(120deg, var(--primary-dark), var(--primary));
  color: #fff;
  padding: 52px 0;
  text-align: center;
}
.cta-band h2 { font-size: 28px; margin-bottom: 10px; }
.cta-band p { color: #cddbe8; margin-bottom: 22px; }

/* ---------- Contact ---------- */
.contact-grid { display: grid; grid-template-columns: 1fr 1.4fr; gap: 44px; }
.info-item { margin-bottom: 22px; }
.info-item h3 { color: var(--primary-dark); font-size: 16px; margin-bottom: 4px; }
.info-item p { color: var(--muted); }
.form-group { margin-bottom: 18px; }
.form-group label {
  display: block;
  font-weight: 600;
  margin-bottom: 6px;
  font-size: 14.5px;
}
.form-group input,
.form-group textarea {
  width: 100%;
  padding: 12px 14px;
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: 15px;
  font-family: inherit;
}
.form-group input:focus, .form-group textarea:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(11, 79, 138, .12);
}
.form-status { margin-top: 14px; font-weight: 600; display: none; }
.form-status.ok { display: block; color: #1a7f37; }
.form-status.err { display: block; color: #c0392b; }
.hp-field { position: absolute; left: -9999px; opacity: 0; }

/* ---------- Footer ---------- */
.site-footer { background: #10202f; color: #9fb3c4; font-size: 14.5px; }
.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr 1.2fr;
  gap: 32px;
  padding: 52px 0 36px;
}
.site-footer h3 { color: #fff; font-size: 16px; margin-bottom: 14px; }
.site-footer a { color: #9fb3c4; }
.site-footer a:hover { color: #fff; }
.site-footer li { margin-bottom: 8px; }
.footer-bottom {
  border-top: 1px solid #1e3548;
  padding: 18px 0;
  font-size: 13px;
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 8px;
}

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 980px) {
  .grid-3, .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .split, .contact-grid, .product-hero { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: repeat(2, 1fr); }
  .hero-content h1 { font-size: 32px; }
}

@media (max-width: 720px) {
  .section { padding: 44px 0; }
  .nav-toggle-label { display: block; }
  .main-nav {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--white);
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow);
  }
  .nav-toggle:checked ~ .main-nav { display: block; }
  .main-nav ul { flex-direction: column; padding: 10px 20px 16px; }
  .main-nav a { padding: 12px 10px; border-bottom: 1px solid var(--bg-light); }
  .logo-text strong { font-size: 14px; }
  .hero { min-height: 340px; }
  .hero-content h1 { font-size: 26px; }
  .hero-content p { font-size: 16px; }
  .btn-outline { margin-left: 0; margin-top: 10px; }
  .grid-2, .grid-3, .grid-4 { grid-template-columns: 1fr; }
  .footer-grid { grid-template-columns: 1fr; gap: 22px; }
  .section-title { font-size: 24px; }
  .page-banner h1 { font-size: 26px; }
  .stats .grid-4 { grid-template-columns: repeat(2, 1fr); }
  .spec-table { font-size: 14px; }
  .spec-table th, .spec-table td { padding: 8px 10px; }
}