/* ============================================
   快连官网 (Kuailian PC) - 主样式表
   SEO优化: 语义化结构、快速加载、移动优先
   ============================================ */

/* --- Reset & Base --- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  font-size: 16px; line-height: 1.8; color: #1e293b; background: #ffffff;
}
a { color: #2563eb; text-decoration: none; transition: color .2s; }
a:hover { color: #1d4ed8; text-decoration: underline; }
img { max-width: 100%; height: auto; vertical-align: middle; }
ul, ol { list-style: none; }
.container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }

/* --- Header --- */
.site-header {
  background: linear-gradient(135deg, #1e293b 0%, #334155 100%);
  position: sticky; top: 0; z-index: 100; box-shadow: 0 2px 12px rgba(0,0,0,.1);
}
.header-inner {
  display: flex; align-items: center; justify-content: space-between;
  height: 68px; max-width: 1200px; margin: 0 auto; padding: 0 20px;
}
.logo { display: flex; align-items: center; gap: 10px; }
.logo-icon {
  width: 36px; height: 36px; background: linear-gradient(135deg, #3b82f6, #2563eb);
  border-radius: 8px; display: flex; align-items: center; justify-content: center;
  color: #fff; font-size: 20px; font-weight: 700;
}
.logo-text { color: #fff; font-size: 22px; font-weight: 700; letter-spacing: 1px; }
.logo-text span { color: #60a5fa; }

.main-nav { display: flex; align-items: center; gap: 32px; }
.main-nav a {
  color: #cbd5e1; font-size: 15px; font-weight: 500; position: relative;
  padding: 4px 0; transition: color .2s;
}
.main-nav a::after {
  content: ''; position: absolute; bottom: -2px; left: 0; width: 0;
  height: 2px; background: #3b82f6; transition: width .2s;
}
.main-nav a:hover, .main-nav a.active { color: #fff; text-decoration: none; }
.main-nav a:hover::after, .main-nav a.active::after { width: 100%; }
.nav-download {
  background: linear-gradient(135deg, #3b82f6, #2563eb) !important;
  color: #fff !important; padding: 8px 20px !important; border-radius: 6px;
  font-weight: 600 !important;
}
.nav-download::after { display: none !important; }
.nav-download:hover { background: linear-gradient(135deg, #2563eb, #1d4ed8) !important; }

.menu-toggle { display: none; flex-direction: column; gap: 5px; cursor: pointer; background: none; border: none; padding: 4px; }
.menu-toggle span { display: block; width: 26px; height: 3px; background: #fff; border-radius: 2px; transition: .3s; }

/* --- Hero Section --- */
.hero {
  background: linear-gradient(135deg, #0f172a 0%, #1e293b 50%, #0f172a 100%);
  padding: 80px 0 60px; text-align: center; position: relative; overflow: hidden;
}
.hero::before {
  content: ''; position: absolute; top: -50%; left: -50%; width: 200%; height: 200%;
  background: radial-gradient(ellipse at 30% 50%, rgba(37,99,235,.08) 0%, transparent 60%),
              radial-gradient(ellipse at 70% 50%, rgba(59,130,246,.06) 0%, transparent 60%);
}
.hero .container { position: relative; z-index: 1; }
.hero h1 {
  font-size: 42px; font-weight: 800; color: #fff; margin-bottom: 20px;
  letter-spacing: 1px;
}
.hero h1 span { background: linear-gradient(135deg, #60a5fa, #3b82f6); -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text; }
.hero p {
  font-size: 18px; color: #94a3b8; max-width: 700px; margin: 0 auto 36px;
  line-height: 1.9;
}
.hero-buttons { display: flex; gap: 16px; justify-content: center; flex-wrap: wrap; }
.btn {
  display: inline-flex; align-items: center; gap: 8px; padding: 14px 36px;
  border-radius: 8px; font-size: 16px; font-weight: 600; cursor: pointer;
  transition: all .25s; border: none; text-decoration: none !important;
}
.btn-primary {
  background: linear-gradient(135deg, #3b82f6, #2563eb); color: #fff;
  box-shadow: 0 4px 16px rgba(37,99,235,.35);
}
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 6px 24px rgba(37,99,235,.45); color: #fff; }
.btn-outline {
  background: transparent; color: #cbd5e1; border: 2px solid #475569;
}
.btn-outline:hover { border-color: #3b82f6; color: #fff; transform: translateY(-2px); }
.hero-stats {
  display: flex; justify-content: center; gap: 48px; margin-top: 48px;
  padding-top: 40px; border-top: 1px solid rgba(255,255,255,.06);
}
.hero-stats dt { font-size: 28px; font-weight: 700; color: #fff; }
.hero-stats dd { font-size: 13px; color: #64748b; margin-top: 4px; }

/* --- Section Common --- */
.section { padding: 70px 0; }
.section-alt { background: #f8fafc; }
.section-title {
  font-size: 30px; font-weight: 700; text-align: center; margin-bottom: 12px;
  color: #0f172a;
}
.section-desc {
  text-align: center; color: #64748b; max-width: 600px; margin: 0 auto 48px;
  font-size: 16px;
}
.section-desc-wide { max-width: 800px; }

/* --- Features Grid --- */
.features-grid {
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px;
}
.feature-card {
  background: #fff; border: 1px solid #e2e8f0; border-radius: 12px;
  padding: 32px 28px; transition: all .25s;
}
.feature-card:hover { transform: translateY(-4px); box-shadow: 0 12px 40px rgba(0,0,0,.08); border-color: #bfdbfe; }
.feature-icon {
  width: 52px; height: 52px; border-radius: 12px;
  background: linear-gradient(135deg, #dbeafe, #bfdbfe);
  display: flex; align-items: center; justify-content: center;
  font-size: 24px; margin-bottom: 18px;
}
.feature-card h3 { font-size: 18px; font-weight: 600; margin-bottom: 10px; color: #0f172a; }
.feature-card p { font-size: 14px; color: #64748b; line-height: 1.8; }

/* --- Download Section --- */
.download-grid {
  display: grid; grid-template-columns: repeat(2, 1fr); gap: 24px; max-width: 800px; margin: 0 auto;
}
.download-card {
  background: #fff; border: 1px solid #e2e8f0; border-radius: 12px;
  padding: 32px; text-align: center; transition: all .25s;
}
.download-card:hover { box-shadow: 0 8px 32px rgba(0,0,0,.08); border-color: #bfdbfe; }
.download-card .os-icon { font-size: 40px; margin-bottom: 12px; }
.download-card h3 { font-size: 18px; font-weight: 600; color: #0f172a; margin-bottom: 6px; }
.download-card .version { font-size: 13px; color: #94a3b8; margin-bottom: 16px; }
.download-card .btn { padding: 10px 28px; font-size: 14px; }
.download-card .file-info { font-size: 12px; color: #94a3b8; margin-top: 10px; }

/* --- Content Page (下载/功能/帮助/关于) --- */
.page-banner {
  background: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
  padding: 60px 0 50px; text-align: center;
}
.page-banner h1 { font-size: 36px; font-weight: 800; color: #fff; margin-bottom: 12px; }
.page-banner p { font-size: 16px; color: #94a3b8; max-width: 600px; margin: 0 auto; }
.breadcrumb { margin-top: 16px; font-size: 13px; color: #64748b; }
.breadcrumb a { color: #94a3b8; }
.breadcrumb a:hover { color: #fff; }
.breadcrumb span { color: #60a5fa; }

.page-content { padding: 60px 0; }
.content-body { max-width: 900px; margin: 0 auto; }
.content-body h2 {
  font-size: 24px; font-weight: 700; color: #0f172a;
  margin: 40px 0 16px; padding-bottom: 10px;
  border-bottom: 2px solid #e2e8f0;
}
.content-body h3 { font-size: 19px; font-weight: 600; color: #1e293b; margin: 28px 0 12px; }
.content-body p { margin-bottom: 16px; color: #475569; line-height: 2; }
.content-body ul, .content-body ol { margin: 12px 0 20px 24px; }
.content-body li { margin-bottom: 8px; color: #475569; line-height: 1.9; list-style: disc; }
.content-body strong { color: #0f172a; }

/* --- FAQ --- */
.faq-list { max-width: 800px; margin: 0 auto; }
.faq-item {
  border: 1px solid #e2e8f0; border-radius: 10px; margin-bottom: 12px;
  overflow: hidden; transition: box-shadow .2s;
}
.faq-item:hover { box-shadow: 0 2px 12px rgba(0,0,0,.06); }
.faq-q {
  padding: 18px 24px; font-size: 16px; font-weight: 600; color: #0f172a;
  cursor: pointer; display: flex; justify-content: space-between; align-items: center;
  background: #fff; user-select: none;
}
.faq-q::after {
  content: '+'; font-size: 20px; color: #94a3b8; font-weight: 400;
  transition: transform .2s;
}
.faq-item.active .faq-q::after { content: '−'; color: #2563eb; }
.faq-a {
  display: none; padding: 0 24px 18px; color: #475569; line-height: 1.9;
}
.faq-item.active .faq-a { display: block; }

/* --- Footer --- */
.site-footer {
  background: #0f172a; color: #94a3b8; padding: 48px 0 32px;
}
.footer-inner {
  display: grid; grid-template-columns: 2fr 1fr 1fr 1fr; gap: 40px;
  max-width: 1200px; margin: 0 auto; padding: 0 20px;
}
.footer-brand .logo-text { font-size: 20px; }
.footer-brand p { margin-top: 12px; font-size: 14px; line-height: 1.8; }
.footer-col h4 { color: #fff; font-size: 15px; margin-bottom: 14px; font-weight: 600; }
.footer-col a { display: block; color: #94a3b8; font-size: 14px; margin-bottom: 8px; }
.footer-col a:hover { color: #60a5fa; text-decoration: none; }
.footer-bottom {
  text-align: center; padding-top: 32px; margin-top: 32px;
  border-top: 1px solid rgba(255,255,255,.06); font-size: 13px;
  max-width: 1200px; margin-left: auto; margin-right: auto; padding-left: 20px; padding-right: 20px;
}

/* --- Features-detail page specific --- */
.feature-detail-grid { display: grid; gap: 32px; }
.feature-detail-item {
  display: grid; grid-template-columns: 80px 1fr; gap: 24px;
  padding: 28px; background: #fff; border: 1px solid #e2e8f0; border-radius: 12px;
}
.feature-detail-num {
  width: 80px; height: 80px; border-radius: 16px;
  background: linear-gradient(135deg, #dbeafe, #bfdbfe);
  display: flex; align-items: center; justify-content: center;
  font-size: 28px; font-weight: 800; color: #2563eb;
}
.feature-detail-text h3 { font-size: 18px; font-weight: 600; color: #0f172a; margin-bottom: 8px; }
.feature-detail-text p { font-size: 14px; color: #64748b; line-height: 1.8; }

/* --- About page --- */
.about-mission {
  text-align: center; max-width: 700px; margin: 0 auto 48px;
  padding: 32px; background: linear-gradient(135deg, #dbeafe, #eff6ff);
  border-radius: 16px;
}
.about-mission h2 { font-size: 22px; color: #1e40af; margin-bottom: 12px; border: none; }
.about-mission p { color: #1e40af; font-size: 16px; line-height: 1.9; }
.about-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; }
.about-card {
  text-align: center; padding: 32px 24px; border: 1px solid #e2e8f0;
  border-radius: 12px; transition: .25s;
}
.about-card:hover { box-shadow: 0 8px 32px rgba(0,0,0,.08); }
.about-card .num { font-size: 36px; font-weight: 800; color: #2563eb; }
.about-card h4 { font-size: 16px; font-weight: 600; margin: 8px 0; color: #0f172a; }
.about-card p { font-size: 13px; color: #64748b; }

/* --- Download page --- */
.download-info { max-width: 800px; margin: 0 auto; text-align: center; }
.download-info h2 { margin-top: 0; }
.download-steps { text-align: left; margin: 32px auto; max-width: 600px; }
.download-steps li { list-style: decimal; margin-bottom: 12px; line-height: 1.8; color: #475569; }
.system-req { background: #f8fafc; border-radius: 12px; padding: 28px; margin-top: 32px; text-align: left; }
.system-req h3 { font-size: 18px; font-weight: 600; color: #0f172a; margin-bottom: 12px; }
.system-req ul { margin: 0 0 0 20px; }

/* --- Responsive --- */
@media (max-width: 768px) {
  .menu-toggle { display: flex; }
  .main-nav {
    display: none; position: absolute; top: 68px; left: 0; right: 0;
    background: #1e293b; flex-direction: column; padding: 20px; gap: 16px;
    border-top: 1px solid rgba(255,255,255,.08);
  }
  .main-nav.open { display: flex; }
  .hero h1 { font-size: 28px; }
  .hero p { font-size: 15px; }
  .hero-stats { flex-direction: column; gap: 24px; }
  .features-grid { grid-template-columns: 1fr; }
  .download-grid { grid-template-columns: 1fr; }
  .footer-inner { grid-template-columns: 1fr 1fr; gap: 24px; }
  .section { padding: 44px 0; }
  .section-title { font-size: 24px; }
  .feature-detail-item { grid-template-columns: 1fr; text-align: center; }
  .feature-detail-num { margin: 0 auto; }
  .about-grid { grid-template-columns: 1fr; }
  .page-banner h1 { font-size: 26px; }
  .content-body h2 { font-size: 20px; }
}

@media (max-width: 480px) {
  .footer-inner { grid-template-columns: 1fr; }
  .hero-buttons { flex-direction: column; align-items: center; }
  .btn { width: 100%; justify-content: center; }
}