/* ============================================================
   优题帮 8ut.cn — 官网样式
   品牌色取自 logo：深蓝 #042252 / 品牌蓝 #0A5CB2 / 品牌绿 #07A04A
   ============================================================ */
:root {
  --deep: #042252;
  --primary: #0A5CB2;
  --primary-d: #063C80;
  --accent: #07A04A;
  --accent-d: #057C38;
  --bg: #F4F8FD;
  --ink: #121E35;
  --sub: #6C7B93;
  --line: #E3EAF4;
  --radius: 22px;
  --shadow: 0 12px 40px rgba(4, 34, 82, .10);
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: "PingFang SC", "Microsoft YaHei", "微软雅黑", "Helvetica Neue", Arial, sans-serif;
  color: var(--ink);
  background: #fff;
  line-height: 1.6;
  overflow-x: hidden;
}
img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }
.container { max-width: 1160px; margin: 0 auto; padding: 0 24px; }
.pc-only { display: inline; }

/* ---------------- 通用按钮 ---------------- */
.btn {
  display: inline-flex; align-items: center; gap: 12px;
  border-radius: 999px; padding: 12px 26px;
  font-size: 15px; font-weight: 600;
  transition: transform .2s ease, box-shadow .2s ease, background .2s ease;
  cursor: pointer; border: none;
}
.btn:hover { transform: translateY(-2px); }
.btn-lg { padding: 14px 28px; }
.btn-xl { padding: 16px 34px; font-size: 16px; }
.btn-ico { width: 24px; height: 24px; flex: 0 0 auto; }
.btn-txt { display: flex; flex-direction: column; align-items: flex-start; line-height: 1.3; }
.btn-txt small { font-weight: 400; font-size: 12px; opacity: .85; }
.btn-green { background: linear-gradient(135deg, #0AB558, var(--accent-d)); color: #fff; box-shadow: 0 10px 26px rgba(7, 160, 74, .35); }
.btn-white { background: #fff; color: var(--primary-d); box-shadow: 0 10px 26px rgba(4, 34, 82, .18); }
.btn-ghost { background: rgba(255,255,255,.12); color: #fff; border: 1.5px solid rgba(255,255,255,.55); backdrop-filter: blur(4px); }
.btn-outline { background: #fff; color: var(--primary); border: 1.5px solid var(--primary); }
.btn-outline:hover { background: var(--bg); }

/* ---------------- 顶部导航 ---------------- */
.nav {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  background: rgba(255,255,255,.9); backdrop-filter: blur(12px);
  transition: box-shadow .25s ease;
}
.nav.scrolled { box-shadow: 0 4px 24px rgba(4,34,82,.10); }
.nav-inner {
  max-width: 1160px; margin: 0 auto; padding: 10px 24px;
  display: flex; align-items: center; justify-content: space-between;
}
.nav-logo { display: flex; align-items: center; gap: 10px; }
.nav-logo-img { width: 138px; height: auto; }
.nav-links { display: flex; align-items: center; gap: 26px; font-size: 15px; font-weight: 500; }
.nav-links a { color: var(--ink); transition: color .2s; position: relative; }
.nav-links a:hover { color: var(--primary); }
.nav-links a.nav-cta {
  background: var(--accent); color: #fff; padding: 9px 20px; border-radius: 999px;
}
.nav-links a.nav-cta:hover { background: var(--accent-d); color: #fff; }
.nav-burger { display: none; background: none; border: none; cursor: pointer; padding: 8px; }
.nav-burger span { display: block; width: 22px; height: 2.5px; background: var(--deep); margin: 4.5px 0; border-radius: 2px; transition: .25s; }

/* ---------------- Hero ---------------- */
.hero {
  position: relative; overflow: hidden;
  background: linear-gradient(35deg, var(--deep) 0%, var(--primary) 100%);
  color: #fff; padding: 150px 0 90px;
}
.hero-blob { position: absolute; border-radius: 50%; filter: blur(2px); opacity: .5; animation: float 8s ease-in-out infinite; }
.hero-blob.b1 { width: 300px; height: 300px; background: rgba(10,181,88,.25); top: -80px; right: 8%; }
.hero-blob.b2 { width: 180px; height: 180px; background: rgba(255,255,255,.10); bottom: 10%; left: 4%; animation-delay: 1.5s; }
.hero-blob.b3 { width: 90px; height: 90px; background: rgba(245,166,35,.45); top: 30%; left: 42%; animation-delay: 3s; }
@keyframes float { 0%,100% { transform: translateY(0); } 50% { transform: translateY(-22px); } }

.hero-grid { display: grid; grid-template-columns: 1.15fr .85fr; gap: 48px; align-items: center; position: relative; }
.hero-kicker { font-size: 14px; letter-spacing: 2px; color: #BFD4F0; margin-bottom: 18px; font-weight: 600; }
.hero-kicker::before { content: ""; display: inline-block; width: 34px; height: 4px; background: var(--accent); border-radius: 2px; margin-right: 12px; vertical-align: middle; }
.hero h1 { font-size: clamp(30px, 4.6vw, 52px); line-height: 1.22; font-weight: 800; }
.hero h1 em { font-style: normal; color: #4ADE80; position: relative; }
.hero-sub { margin-top: 18px; font-size: 17px; color: #BFD4F0; }
.hero-actions { display: flex; gap: 16px; margin-top: 34px; flex-wrap: wrap; }
.hero-note { margin-top: 18px; font-size: 13.5px; color: #BFD4F0; }

/* 手机样机（真实 APP 截图，无边框） */
.hero-visual { display: flex; justify-content: center; }
.phone-shot {
  width: 300px; display: block; border-radius: 24px;
  box-shadow: 0 30px 80px rgba(0,0,0,.35);
  animation: bob 4.5s ease-in-out infinite;
}
@keyframes bob { 0%,100% { transform: translateY(0) rotate(-1.5deg); } 50% { transform: translateY(-14px) rotate(1.5deg); } }

/* ---------------- 通用 Section ---------------- */
.section { padding: 96px 0; }
.sec-alt { background: var(--bg); }
.sec-dark { background: linear-gradient(35deg, var(--deep), var(--primary-d)); color: #fff; }
.sec-head { text-align: center; max-width: 720px; margin: 0 auto 56px; }
.sec-head.left { text-align: left; margin: 0 0 24px; }
.sec-line { display: block; width: 34px; height: 4px; background: var(--accent); border-radius: 2px; margin: 0 auto 18px; }
.sec-head.left .sec-line { margin-left: 0; }
.sec-line.green { background: var(--accent); }
.sec-head h2 { font-size: clamp(26px, 3.4vw, 38px); font-weight: 800; }
.sec-head p { margin-top: 12px; color: var(--sub); font-size: 15.5px; }
.sec-dark .sec-head p { color: #BFD4F0; }

/* ---------------- 功能链路 ---------------- */
.flow { display: flex; align-items: stretch; gap: 10px; }
.flow-card {
  flex: 1; background: #fff; border-radius: var(--radius); padding: 30px 22px;
  box-shadow: var(--shadow); text-align: center;
  border-top: 5px solid transparent;
  transition: transform .25s ease, border-color .25s;
}
.flow-card:hover { transform: translateY(-8px); border-top-color: var(--accent); }
.flow-ico {
  width: 64px; height: 64px; border-radius: 20px;
  display: flex; align-items: center; justify-content: center; margin: 0 auto 16px;
  background: color-mix(in srgb, var(--c, #0A5CB2) 14%, #fff);
}
.flow-ico svg { width: 30px; height: 30px; color: var(--c, #0A5CB2); }
.flow-card h3 { font-size: 18px; margin-bottom: 8px; }
.flow-card p { font-size: 13.5px; color: var(--sub); }
.flow-arrow { align-self: center; flex: 0 0 auto; color: var(--accent); }
.flow-arrow svg { width: 22px; height: 22px; display: block; }

/* ---------------- AI 千人千题 ---------------- */
.ai-grid { display: grid; grid-template-columns: .9fr 1.1fr; gap: 56px; align-items: center; }
.ai-label { font-size: 14px; font-weight: 700; letter-spacing: 2px; color: var(--accent-d); margin-bottom: 10px; }
.ai-title { font-size: clamp(48px, 7vw, 84px); font-weight: 900; color: var(--primary-d); line-height: 1.05; }
.ai-desc { margin-top: 16px; color: var(--sub); font-size: 16px; }
.ai-list { display: grid; gap: 16px; }
.ai-item {
  background: #fff; border-radius: 18px; padding: 20px 24px; box-shadow: var(--shadow);
  display: grid; grid-template-columns: auto 1fr; gap: 6px 16px; align-items: baseline;
  border-left: 5px solid var(--accent);
}
.ai-item b { font-size: 16.5px; color: var(--primary-d); }
.ai-item span { font-size: 14px; color: var(--sub); grid-column: 1 / -1; }

/* ---------------- 四大优势 ---------------- */
.adv-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 22px; }
.adv-card {
  background: #fff; border: 1.5px solid var(--line); border-radius: var(--radius);
  padding: 30px 24px; transition: transform .25s, box-shadow .25s, border-color .25s;
}
.adv-card:hover { transform: translateY(-6px); box-shadow: var(--shadow); border-color: transparent; }
.adv-num { font-size: 40px; font-weight: 900; color: var(--accent); opacity: .35; line-height: 1; }
.adv-card h3 { font-size: 18px; margin: 14px 0 8px; }
.adv-card p { font-size: 13.5px; color: var(--sub); }

/* ---------------- 定价 ---------------- */
.price-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; align-items: end; max-width: 960px; margin: 0 auto; }
.price-card {
  background: #fff; border-radius: var(--radius); padding: 36px 30px; text-align: center;
  box-shadow: var(--shadow); border: 1.5px solid var(--line); position: relative;
}
.price-card h3 { font-size: 18px; color: var(--primary-d); }
.price { font-size: 52px; font-weight: 900; color: var(--ink); margin-top: 10px; line-height: 1; }
.price small { font-size: 22px; font-weight: 700; vertical-align: super; margin-right: 2px; }
.price-unit { color: var(--sub); font-size: 13.5px; margin: 8px 0 20px; }
.price-card ul { list-style: none; text-align: left; margin-bottom: 26px; display: grid; gap: 10px; }
.price-card li { font-size: 14px; color: var(--ink); padding-left: 26px; position: relative; }
.price-card li::before { content: "✓"; position: absolute; left: 0; color: var(--accent); font-weight: 800; }
.price-hot {
  background: linear-gradient(160deg, var(--primary-d), var(--deep)); color: #fff;
  border: none; transform: scale(1.05); z-index: 2; padding: 44px 30px 40px;
}
.price-hot h3 { color: #fff; }
.price-hot .price { color: #4ADE80; }
.price-hot .price-unit { color: #BFD4F0; }
.price-hot li { color: #EAF2FC; }
.price-hot li::before { color: #4ADE80; }
.hot-tag {
  position: absolute; top: -16px; left: 50%; transform: translateX(-50%);
  background: var(--accent); color: #fff; font-size: 13px; font-weight: 700;
  padding: 6px 18px; border-radius: 999px; box-shadow: 0 8px 20px rgba(7,160,74,.4);
  white-space: nowrap;
}

/* ---------------- 公司简介 ---------------- */
.about-grid { display: grid; grid-template-columns: 1.2fr .8fr; gap: 56px; align-items: center; }
.about-text > p { margin-bottom: 14px; color: #33415C; font-size: 15px; }
.about-points { display: grid; gap: 14px; margin: 24px 0 12px; }
.about-point {
  background: var(--bg); border-radius: 16px; padding: 14px 20px;
  display: grid; grid-template-columns: auto 1fr; gap: 4px 14px; align-items: baseline;
}
.about-point b { color: var(--primary-d); font-size: 15px; }
.about-point span { font-size: 13.5px; color: var(--sub); grid-column: 1 / -1; }
.about-company {
  margin-top: 20px; background: #fff; border: 1.5px solid var(--line);
  border-left: 5px solid var(--accent); border-radius: 14px; padding: 16px 20px;
}
.about-company b { display: block; font-size: 14.5px; color: var(--primary-d); margin-bottom: 6px; }
.about-company span { font-size: 13px; color: var(--sub); line-height: 1.7; }
.about-logo-board {
  background: #fff; border-radius: 28px; padding: 40px; box-shadow: var(--shadow);
  border: 1.5px solid var(--line); display: flex; align-items: center; justify-content: center;
}

/* ---------------- 渠道合作 ---------------- */
.partner-grid { display: grid; grid-template-columns: .85fr 1.15fr; gap: 44px; align-items: start; }
.partner-visual { border-radius: var(--radius); overflow: hidden; box-shadow: 0 20px 50px rgba(0,0,0,.3); }
.partner-visual img { width: 100%; }
/* 渠道合作方案卡 */
.plan-card {
  margin-top: 24px; background: #fff; border-radius: var(--radius);
  padding: 28px 30px; box-shadow: 0 20px 50px rgba(0,0,0,.3);
}
.plan-label {
  display: inline-block; background: var(--accent); color: #fff; font-size: 12.5px;
  font-weight: 700; padding: 4px 14px; border-radius: 999px; margin-bottom: 12px;
}
.plan-price { font-size: 54px; font-weight: 900; color: var(--primary-d); line-height: 1; }
.plan-price small { font-size: 24px; vertical-align: super; margin-right: 2px; }
.plan-unit { color: var(--sub); font-size: 13.5px; margin: 6px 0 16px; }
.plan-card ul { list-style: none; display: grid; gap: 10px; }
.plan-card li { font-size: 13.5px; color: var(--ink); padding-left: 24px; position: relative; line-height: 1.55; }
.plan-card li::before {
  content: ""; position: absolute; left: 0; top: 7px; width: 14px; height: 14px;
  border-radius: 50%; background: var(--accent); opacity: .9;
  -webkit-mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='black' stroke-width='3' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M20 6 9 17l-5-5'/%3E%3C/svg%3E") center/contain no-repeat;
          mask: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='black' stroke-width='3' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M20 6 9 17l-5-5'/%3E%3C/svg%3E") center/contain no-repeat;
}
.plan-card li b { color: var(--accent-d); }
.partner-right h3 { font-size: 19px; margin: 30px 0 16px; color: #fff; }
.partner-right h3:first-child { margin-top: 0; }
.partner-list { list-style: none; display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.partner-list li {
  background: rgba(255,255,255,.08); border-radius: 16px; padding: 16px 20px;
  border-left: 4px solid var(--accent);
}
.partner-list b { display: block; font-size: 15px; margin-bottom: 4px; }
.partner-list span { font-size: 13px; color: #BFD4F0; }
.steps { list-style: none; display: flex; gap: 8px; counter-reset: step; }
.steps li {
  flex: 1; background: rgba(255,255,255,.08); border-radius: 14px; padding: 14px 8px;
  text-align: center; font-size: 13.5px; font-weight: 600;
}
.steps li i {
  display: block; width: 30px; height: 30px; border-radius: 50%; background: var(--accent);
  color: #fff; font-style: normal; font-weight: 800; line-height: 30px; margin: 0 auto 8px; font-size: 14px;
}
.support-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }
.support-card {
  background: rgba(255,255,255,.08); border-radius: 16px; padding: 18px 20px;
}
.support-card svg { width: 26px; height: 26px; color: #4ADE80; margin-bottom: 10px; }
.support-card b { display: block; font-size: 15px; margin-bottom: 4px; }
.support-card span { font-size: 13px; color: #BFD4F0; }
.qr-card {
  margin-top: 24px; background: #fff; border-radius: var(--radius);
  padding: 22px 26px; display: flex; gap: 20px; align-items: center;
}
.qr-card img { width: 128px; height: 128px; border-radius: 12px; flex: 0 0 auto; }
.qr-txt b { display: block; font-size: 16.5px; color: var(--primary-d); margin-bottom: 6px; }
.qr-txt span { font-size: 13.5px; color: var(--sub); }
.footer-qr { display: flex; align-items: center; gap: 12px; margin-bottom: 14px; }
.footer-qr img { width: 96px; height: 96px; border-radius: 10px; background: #fff; padding: 4px; }
.footer-qr p { font-size: 13px; line-height: 1.6; }
.partner-cta { margin-top: 30px; }

/* ---------------- 下载区 ---------------- */
.sec-download { background: linear-gradient(35deg, var(--primary) 0%, var(--deep) 100%); color: #fff; }
.dl-wrap { display: grid; grid-template-columns: 1.3fr .7fr; gap: 40px; align-items: center; }
.dl-left h2 { font-size: clamp(28px, 4vw, 44px); font-weight: 800; }
.dl-left > p { margin-top: 14px; color: #BFD4F0; font-size: 15.5px; max-width: 560px; }
.dl-buttons { display: flex; gap: 18px; margin-top: 32px; flex-wrap: wrap; }
.dl-note { margin-top: 18px; font-size: 13px; color: #9FB6D9; }
.dl-right { display: flex; justify-content: center; }
.dl-badge {
  width: 200px; height: 200px; border-radius: 44px;
  box-shadow: 0 30px 70px rgba(0,0,0,.4);
  animation: bob 4.5s ease-in-out infinite;
}

/* ---------------- 页脚 ---------------- */
.footer { background: #0A1830; color: #9FB6D9; padding-top: 70px; }
.footer-grid { display: grid; grid-template-columns: 1.4fr 1fr 1fr 1.3fr; gap: 40px; padding-bottom: 50px; }
.footer-logo-board { background: #fff; border-radius: 16px; padding: 14px 20px; width: fit-content; margin-bottom: 16px; }
.footer-logo-board img { height: 44px; }
.footer-brand p { font-size: 14px; }
.footer-col h4 { color: #fff; font-size: 15px; margin-bottom: 16px; }
.footer-col a { display: block; font-size: 14px; margin-bottom: 10px; transition: color .2s; }
.footer-col a:hover { color: #4ADE80; }
.footer-contact { font-size: 14px; line-height: 1.9; }
.footer-contact b { color: #fff; }
.footer-bottom { border-top: 1px solid rgba(255,255,255,.1); padding: 20px 0; font-size: 12.5px; }
.footer-bottom .container { display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.beian a:hover { color: #4ADE80; }

/* ---------------- 入场动画 ---------------- */
.reveal { opacity: 0; transform: translateY(28px); transition: opacity .7s ease, transform .7s ease; }
.reveal.visible { opacity: 1; transform: none; }

/* ---------------- 微信/QQ 打开引导 ---------------- */
.wx-mask {
  display: none; position: fixed; inset: 0; z-index: 200;
  background: rgba(4, 12, 28, .88);
}
.wx-mask.show { display: flex; align-items: center; justify-content: center; }
.wx-tip { position: absolute; top: 0; left: 0; right: 0; bottom: 0; }
.wx-target {
  position: absolute; top: 16px; right: 20px;
  width: 44px; height: 30px; border-radius: 8px;
  background: rgba(255,255,255,.18); border: 1.5px dashed rgba(255,255,255,.7);
  color: #fff; font-size: 16px; font-weight: 800; letter-spacing: 2px;
  display: flex; align-items: center; justify-content: center; line-height: 0;
}
.wx-arrow {
  position: absolute; top: 58px; right: 34px;
  width: 40px; height: 40px; color: #fff;
  animation: wxPoint 1.4s ease-in-out infinite;
}
@keyframes wxPoint { 0%,100% { transform: translate(0,0); opacity: .7; } 50% { transform: translate(5px,-5px); opacity: 1; } }
.wx-card {
  position: absolute; top: 128px; left: 50%; transform: translateX(-50%);
  width: min(84vw, 320px); background: #fff; color: var(--ink);
  border-radius: 20px; padding: 26px 24px 22px; text-align: center;
  box-shadow: 0 24px 60px rgba(0,0,0,.45);
}
.wx-title { font-size: 16.5px; font-weight: 700; color: var(--primary-d); line-height: 1.5; }
.wx-title b {
  background: var(--bg); border: 1.5px solid var(--line); border-radius: 8px;
  padding: 1px 10px; margin: 0 2px;
}
.wx-step { margin-top: 12px; font-size: 14.5px; line-height: 1.8; color: #33415C; }
.wx-step b { color: var(--accent-d); }
.wx-close {
  margin-top: 18px; width: 100%; padding: 11px 0; border: none; border-radius: 999px;
  background: var(--accent); color: #fff; font-size: 15px; font-weight: 600; cursor: pointer;
}
.wx-close:active { background: var(--accent-d); }

/* ---------------- 移动端底部导航 ---------------- */
.tabbar { display: none; }
@media (max-width: 960px) {
  body { padding-bottom: calc(62px + env(safe-area-inset-bottom)); }
  .tabbar {
    display: flex; position: fixed; bottom: 0; left: 0; right: 0; z-index: 99;
    background: rgba(255,255,255,.97); backdrop-filter: blur(12px);
    border-top: 1px solid var(--line);
    padding: 6px 4px calc(6px + env(safe-area-inset-bottom));
    box-shadow: 0 -6px 24px rgba(4,34,82,.08);
  }
  .tab {
    flex: 1; display: flex; flex-direction: column; align-items: center; gap: 3px;
    font-size: 11px; color: var(--sub); padding: 3px 0; transition: color .2s;
  }
  .tab svg { width: 22px; height: 22px; }
  .tab.active { color: var(--primary); font-weight: 600; }
  .tab-cta.active { color: var(--accent-d); }
}

/* ---------------- 响应式 ---------------- */
@media (max-width: 960px) {
  .pc-only { display: none; }
  .hero { padding: 120px 0 70px; }
  .hero-grid { grid-template-columns: 1fr; text-align: center; }
  .hero-actions, .hero-visual { justify-content: center; }
  .hero-kicker::before { display: block; margin: 0 auto 10px; }
  .ai-grid, .about-grid, .partner-grid, .dl-wrap { grid-template-columns: 1fr; }
  .adv-grid { grid-template-columns: 1fr 1fr; }
  .price-grid { grid-template-columns: 1fr; max-width: 420px; }
  .price-hot { transform: none; }
  .flow { flex-direction: column; }
  .flow-arrow { transform: rotate(90deg); margin: 2px auto; }
  .footer-grid { grid-template-columns: 1fr 1fr; }
  .nav-burger { display: block; }
  .nav-links {
    position: fixed; top: 86px; left: 0; right: 0; background: #fff;
    flex-direction: column; padding: 24px; gap: 18px;
    box-shadow: 0 20px 40px rgba(4,34,82,.15);
    transform: translateY(-130%); transition: transform .3s ease;
  }
  .nav-links.open { transform: none; }
}
@media (max-width: 560px) {
  .adv-grid, .partner-list, .support-grid, .footer-grid { grid-template-columns: 1fr; }
  .steps { flex-wrap: wrap; }
  .steps li { flex: 1 1 30%; }
  .btn-xl { width: 100%; justify-content: center; }
  .hero-actions .btn { width: 100%; justify-content: center; }
}