/* =============================================================
   北邮社杯主页样式 —— 深藏青 × 科技蓝 × 竞赛红
   设计语言参考权威赛事官网：大标题、深色主视觉、数据看板、时间轴
   ============================================================= */

:root {
  --navy-900: #081A33;
  --navy-800: #0B2547;
  --navy-700: #10315C;
  --blue-500: #2E7CF6;
  --blue-400: #5B9BFF;
  --red-500: #C8102E;
  --gold-400: #F2C14E;
  --ink: #1C2B3A;
  --muted: #5F7186;
  --line: #E3EAF2;
  --bg-soft: #F5F8FC;
  --white: #FFFFFF;
  --radius: 14px;
  --shadow: 0 10px 30px rgba(11, 37, 71, .08);
  --font: "PingFang SC", "Microsoft YaHei", "Helvetica Neue", "Noto Sans SC", sans-serif;
}

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }

body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--white);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

.wrap { max-width: 1120px; margin: 0 auto; padding: 0 24px; }

/* ============ 按钮体系 ============ */
.btn {
  display: inline-flex; align-items: center; justify-content: center;
  border-radius: 999px; text-decoration: none; cursor: pointer;
  font-weight: 600; letter-spacing: .05em;
  transition: transform .25s, box-shadow .25s, background .25s, color .25s;
  border: none;
}
.btn:active { transform: translateY(1px); }
.btn-primary {
  background: linear-gradient(120deg, var(--red-500), #E4402F);
  color: #fff;
  box-shadow: 0 8px 22px rgba(200, 16, 46, .35);
}
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 12px 28px rgba(200, 16, 46, .45); }
.btn-ghost {
  color: #fff; border: 1.5px solid rgba(255, 255, 255, .55);
  background: rgba(255, 255, 255, .06);
  backdrop-filter: blur(6px);
}
.btn-ghost:hover { background: rgba(255, 255, 255, .16); border-color: #fff; }
.btn-light {
  background: #fff; color: var(--navy-800);
  box-shadow: 0 10px 26px rgba(0, 0, 0, .25);
}
.btn-light:hover { transform: translateY(-2px); }
.btn-sm { padding: 9px 22px; font-size: 14px; }
.btn-lg { padding: 15px 42px; font-size: 17px; }

/* ============ 顶部导航 ============ */
.nav {
  position: fixed; inset: 0 0 auto 0; z-index: 100;
  transition: background .3s, box-shadow .3s, padding .3s;
  padding: 14px 0;
}
.nav.scrolled {
  background: rgba(8, 26, 51, .88);
  backdrop-filter: blur(14px);
  box-shadow: 0 6px 24px rgba(0, 0, 0, .25);
  padding: 8px 0;
}
.nav-inner {
  max-width: 1180px; margin: 0 auto; padding: 0 24px;
  display: flex; align-items: center; gap: 32px;
}
.nav-logo { display: flex; align-items: center; gap: 10px; text-decoration: none; }
.logo-mark {
  width: 38px; height: 38px; border-radius: 10px;
  background: linear-gradient(135deg, var(--red-500), #F0523C);
  color: #fff; font-weight: 800; font-size: 19px;
  display: flex; align-items: center; justify-content: center;
  box-shadow: 0 6px 16px rgba(200, 16, 46, .4);
}
.logo-img {
  width: 38px; height: 38px;
  border-radius: 10px;
  object-fit: cover;
  box-shadow: 0 6px 16px rgba(11, 37, 71, .3);
}
.footer-brand .logo-img { box-shadow: none; }
/* 赛事"邮"字标：替代赞助单位 Logo，避免误解为赛事标志 */
.logo-mark {
  width: 38px; height: 38px; border-radius: 10px; flex-shrink: 0;
  background: linear-gradient(135deg, var(--red-500), #F0523C);
  color: #fff; font-weight: 800; font-size: 19px;
  display: flex; align-items: center; justify-content: center;
  box-shadow: 0 6px 16px rgba(200, 16, 46, .4);
}
.footer-brand .logo-mark { box-shadow: none; }
.sponsor-logo img {
  width: 100%; height: 100%; object-fit: contain; border-radius: 18px; background: #fff;
}
.logo-text { color: #fff; font-size: 18px; font-weight: 700; letter-spacing: .08em; }
.logo-text em {
  font-style: normal; font-size: 12px; font-weight: 600;
  color: var(--gold-400); margin-left: 8px; letter-spacing: .2em;
}
.nav-links { display: flex; gap: 26px; margin-left: auto; }
.nav-links a {
  color: rgba(255, 255, 255, .82); text-decoration: none; font-size: 15px;
  position: relative; padding: 4px 0; transition: color .2s;
}
.nav-links a::after {
  content: ""; position: absolute; left: 0; bottom: -2px;
  width: 0; height: 2px; background: var(--red-500); transition: width .25s;
}
.nav-links a:hover { color: #fff; }
.nav-links a:hover::after { width: 100%; }

/* ============ 主视觉 Hero ============ */
.hero {
  position: relative; overflow: hidden;
  min-height: 92vh;
  background:
    radial-gradient(1100px 500px at 78% -10%, rgba(46, 124, 246, .35), transparent 60%),
    radial-gradient(800px 420px at 8% 110%, rgba(200, 16, 46, .22), transparent 60%),
    linear-gradient(160deg, var(--navy-900) 0%, var(--navy-800) 55%, var(--navy-700) 100%);
  color: #fff;
  display: flex; align-items: center; justify-content: center;
  text-align: center;
}
#particles { position: absolute; inset: 0; width: 100%; height: 100%; }
.hero-glow {
  position: absolute; left: 50%; top: 42%; transform: translate(-50%, -50%);
  width: 760px; height: 760px; border-radius: 50%;
  background: radial-gradient(circle, rgba(46, 124, 246, .18), transparent 65%);
  pointer-events: none;
  animation: breathe 6s ease-in-out infinite;
}
@keyframes breathe {
  0%, 100% { transform: translate(-50%, -50%) scale(1); opacity: .9; }
  50% { transform: translate(-50%, -50%) scale(1.12); opacity: .6; }
}
.hero-inner { position: relative; z-index: 2; padding: 120px 24px 90px; max-width: 900px; }

.hero-badge {
  display: inline-block;
  padding: 8px 22px; border-radius: 999px;
  border: 1px solid rgba(242, 193, 78, .55);
  color: var(--gold-400); font-size: 14px; letter-spacing: .18em;
  background: rgba(242, 193, 78, .08);
  margin-bottom: 30px;
}
.hero-title {
  font-size: clamp(44px, 7.2vw, 76px);
  font-weight: 800; letter-spacing: .06em; line-height: 1.25;
  text-shadow: 0 12px 40px rgba(0, 0, 0, .35);
}
.hero-title .dot { color: var(--red-500); margin: 0 .12em; }
.hero-sub {
  margin-top: 26px; font-size: clamp(15px, 1.8vw, 19px);
  color: rgba(255, 255, 255, .82); letter-spacing: .04em;
}
.hero-actions { margin-top: 44px; display: flex; gap: 18px; justify-content: center; flex-wrap: wrap; }
.hero-meta {
  margin-top: 52px; display: flex; align-items: center; justify-content: center;
  gap: 18px; font-size: 14px; color: rgba(255, 255, 255, .62);
}
.hero-meta .divider { width: 1px; height: 14px; background: rgba(255, 255, 255, .3); }
.pulse {
  display: inline-block; width: 8px; height: 8px; border-radius: 50%;
  background: #37D67A; margin-right: 8px;
  box-shadow: 0 0 0 0 rgba(55, 214, 122, .6);
  animation: pulse 2s infinite;
}
@keyframes pulse {
  0% { box-shadow: 0 0 0 0 rgba(55, 214, 122, .55); }
  70% { box-shadow: 0 0 0 10px rgba(55, 214, 122, 0); }
  100% { box-shadow: 0 0 0 0 rgba(55, 214, 122, 0); }
}

/* 滚动提示 */
.scroll-hint {
  position: absolute; left: 50%; bottom: 26px; transform: translateX(-50%);
  width: 26px; height: 42px; border: 2px solid rgba(255, 255, 255, .45);
  border-radius: 14px; z-index: 2;
}
.scroll-hint span {
  position: absolute; left: 50%; top: 8px; transform: translateX(-50%);
  width: 4px; height: 8px; border-radius: 2px; background: #fff;
  animation: drop 1.8s ease-in-out infinite;
}
@keyframes drop {
  0% { opacity: 1; top: 8px; }
  70% { opacity: 0; top: 24px; }
  100% { opacity: 0; top: 8px; }
}

/* ============ 数据看板 ============ */
.stats {
  background: var(--white);
  padding: 44px 0;
}
.stats-grid {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px;
  background: var(--white);
  border: 1px solid var(--line); border-radius: 18px;
  box-shadow: var(--shadow);
  padding: 36px 20px;
}
.stat { text-align: center; }
.stat-num {
  font-size: clamp(30px, 4vw, 44px); font-weight: 800; color: var(--navy-800);
  font-variant-numeric: tabular-nums;
}
.stat-num i { font-style: normal; font-size: .45em; color: var(--blue-500); margin-left: 4px; font-weight: 700; }
.stat-label { color: var(--muted); font-size: 14px; margin-top: 4px; }

/* ============ 通用节 ============ */
.section { padding: 96px 0; }
.section-alt { background: var(--bg-soft); }
.sec-head { text-align: center; margin-bottom: 56px; }
.sec-tag {
  display: inline-block; font-size: 12px; letter-spacing: .32em;
  color: var(--blue-500); font-weight: 700; margin-bottom: 12px;
}
.sec-head h2 { font-size: clamp(26px, 3.4vw, 36px); color: var(--navy-800); letter-spacing: .04em; }
.sec-head h2::after {
  content: ""; display: block; width: 46px; height: 4px; border-radius: 2px;
  background: linear-gradient(90deg, var(--red-500), var(--gold-400));
  margin: 16px auto 0;
}
.sec-head p { color: var(--muted); margin-top: 14px; font-size: 15px; }

/* ============ 特色卡片 ============ */
.feature-grid {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 22px;
}
.feature-card {
  background: var(--white); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 30px 24px;
  transition: transform .3s, box-shadow .3s, border-color .3s;
}
.feature-card:hover {
  transform: translateY(-6px);
  box-shadow: 0 18px 40px rgba(11, 37, 71, .14);
  border-color: rgba(46, 124, 246, .4);
}
.feature-icon {
  width: 52px; height: 52px; border-radius: 12px;
  background: linear-gradient(135deg, rgba(46, 124, 246, .12), rgba(46, 124, 246, .04));
  color: var(--blue-500);
  display: flex; align-items: center; justify-content: center;
  margin-bottom: 18px;
}
.feature-icon svg { width: 26px; height: 26px; }
.feature-card h3 { font-size: 18px; color: var(--navy-800); margin-bottom: 8px; }
.feature-card p { font-size: 14px; color: var(--muted); }

/* ============ 报名流程 ============ */
.steps {
  display: grid; grid-template-columns: repeat(4, 1fr); gap: 22px;
  counter-reset: step;
}
.step {
  position: relative; background: var(--white);
  border: 1px solid var(--line); border-radius: var(--radius);
  padding: 30px 22px 26px;
  transition: transform .3s, box-shadow .3s;
}
.step:hover { transform: translateY(-6px); box-shadow: var(--shadow); }
.step-no {
  font-size: 34px; font-weight: 800; line-height: 1;
  background: linear-gradient(120deg, var(--blue-500), #7DB4FF);
  -webkit-background-clip: text; background-clip: text; color: transparent;
  margin-bottom: 14px;
}
.step h3 { font-size: 17px; color: var(--navy-800); margin-bottom: 8px; }
.step p { font-size: 14px; color: var(--muted); }
/* 步骤间连接线 */
.step:not(:last-child)::after {
  content: ""; position: absolute; top: 42px; right: -22px;
  width: 22px; height: 2px;
  background: repeating-linear-gradient(90deg, var(--blue-400) 0 6px, transparent 6px 12px);
}

/* ============ 时间轴 ============ */
.timeline { max-width: 760px; margin: 0 auto; position: relative; padding-left: 30px; }
.timeline::before {
  content: ""; position: absolute; left: 7px; top: 8px; bottom: 8px;
  width: 2px; background: linear-gradient(180deg, var(--blue-500), var(--red-500));
  border-radius: 1px;
}
.tl-item { position: relative; padding-bottom: 30px; }
.tl-item:last-child { padding-bottom: 0; }
.tl-item::before {
  content: ""; position: absolute; left: -30px; top: 6px;
  width: 14px; height: 14px; border-radius: 50%;
  background: var(--white); border: 3px solid var(--blue-500);
  box-shadow: 0 0 0 4px rgba(46, 124, 246, .15);
}
.tl-date {
  font-size: 13px; font-weight: 700; letter-spacing: .08em;
  color: var(--blue-500); margin-bottom: 8px;
}
.tl-card {
  background: var(--white); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 20px 24px;
  transition: transform .25s, box-shadow .25s;
}
.tl-card:hover { transform: translateX(6px); box-shadow: var(--shadow); }
.tl-card h3 { font-size: 17px; color: var(--navy-800); margin-bottom: 6px; }
.tl-card p { font-size: 14px; color: var(--muted); }

/* ============ 赞助企业 ============ */
.sponsor-grid {
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 22px;
}
.sponsor-card {
  position: relative; text-align: center;
  background: var(--white); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 36px 24px 30px;
  transition: transform .3s, box-shadow .3s;
}
.sponsor-card:hover { transform: translateY(-6px); box-shadow: var(--shadow); }
.sponsor-card.primary {
  border-color: rgba(200, 16, 46, .45);
  background: linear-gradient(180deg, #FFF9F9, #fff);
  box-shadow: 0 14px 34px rgba(200, 16, 46, .12);
}
.sponsor-badge {
  position: absolute; top: -12px; left: 50%; transform: translateX(-50%);
  background: linear-gradient(120deg, var(--red-500), #E4402F);
  color: #fff; font-size: 12px; font-weight: 600;
  padding: 4px 16px; border-radius: 999px; white-space: nowrap;
  box-shadow: 0 6px 14px rgba(200, 16, 46, .35);
}
.sponsor-logo {
  width: 72px; height: 72px; margin: 0 auto 18px;
  border-radius: 18px;
  background: linear-gradient(135deg, var(--navy-700), var(--blue-500));
  color: #fff; font-size: 30px; font-weight: 800;
  display: flex; align-items: center; justify-content: center;
  box-shadow: 0 10px 22px rgba(11, 37, 71, .25);
}
.sponsor-card.primary .sponsor-logo {
  background: linear-gradient(135deg, var(--red-500), #F0523C);
}
.sponsor-card h3 { font-size: 16px; color: var(--navy-800); margin-bottom: 6px; }
.sponsor-card p { font-size: 13px; color: var(--muted); }

/* ============ CTA ============ */
.cta {
  background:
    radial-gradient(700px 300px at 20% 0%, rgba(46, 124, 246, .3), transparent 60%),
    linear-gradient(140deg, var(--navy-800), var(--navy-900));
  color: #fff; text-align: center; padding: 88px 0;
}
.cta-inner h2 { font-size: clamp(26px, 3.6vw, 38px); letter-spacing: .05em; }
.cta-inner p { color: rgba(255, 255, 255, .75); margin: 14px 0 34px; }

/* ============ 页脚 ============ */
.footer { background: var(--navy-900); color: rgba(255, 255, 255, .66); padding: 42px 0; }
.footer-inner {
  display: flex; align-items: center; justify-content: space-between;
  gap: 24px; flex-wrap: wrap;
}
.footer-brand { display: flex; align-items: center; gap: 14px; }
.footer-brand strong { color: #fff; font-size: 16px; letter-spacing: .05em; }
.footer-brand p { font-size: 13px; margin-top: 2px; }
.footer-meta { display: flex; flex-direction: column; gap: 6px; font-size: 12px; text-align: right; }

/* ============ 滚动入场动效 ============ */
.reveal { opacity: 0; transform: translateY(26px); transition: opacity .7s ease, transform .7s ease; }
.reveal.visible { opacity: 1; transform: none; }
/* 同组元素依次延迟 */
.feature-grid .reveal:nth-child(2), .steps .reveal:nth-child(2) { transition-delay: .1s; }
.feature-grid .reveal:nth-child(3), .steps .reveal:nth-child(3) { transition-delay: .2s; }
.feature-grid .reveal:nth-child(4), .steps .reveal:nth-child(4) { transition-delay: .3s; }

/* ============ 响应式 ============ */
@media (max-width: 960px) {
  .feature-grid, .steps, .sponsor-grid { grid-template-columns: repeat(2, 1fr); }
  .stats-grid { grid-template-columns: repeat(2, 1fr); row-gap: 32px; }
  .step:not(:last-child)::after { display: none; }
}
@media (max-width: 640px) {
  .nav-links { display: none; }
  .hero { min-height: 86vh; }
  .hero-actions .btn-lg { padding: 13px 30px; font-size: 15px; }
  .feature-grid, .steps, .sponsor-grid { grid-template-columns: 1fr; }
  .stats-grid { grid-template-columns: repeat(2, 1fr); padding: 26px 12px; }
  .section { padding: 68px 0; }
  .footer-inner { flex-direction: column; align-items: flex-start; }
  .footer-meta { text-align: left; }
  .br-wide { display: none; }
}
@media (prefers-reduced-motion: reduce) {
  .reveal { opacity: 1; transform: none; transition: none; }
  .hero-glow, .scroll-hint span, .pulse { animation: none; }
}

/* ============ 顶栏展示图（甲方提供 banner） ============ */
.hero-banner { position: relative; z-index: 1; }
.hero-banner img {
  display: block; width: 100%; object-fit: cover;
  max-height: 520px; object-position: center;
}
.hero-bar {
  position: relative; z-index: 5;
  background: linear-gradient(160deg, var(--navy-900) 0%, var(--navy-800) 60%, var(--navy-700) 100%);
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  gap: 14px; padding: 26px 24px;
}
.hero-bar .btn-lg { flex: 0 0 auto; }
.hero-bar .btn-row {
  display: flex; align-items: center; justify-content: center;
  gap: 22px; flex-wrap: wrap;
}
.hero-bar .hero-meta {
  color: rgba(255,255,255,.8); font-size: 14px;
  display: flex; align-items: center; justify-content: center; gap: 12px;
}
.hero-banner .btn-ghost { color: #fff; }
@media (max-width: 720px) {
  .hero-bar { gap: 12px; padding: 20px 16px; }
  .hero-bar .btn-row { gap: 14px; }
}