/* 《万物是如何运转的》全站设计系统 */
:root {
  --blue: #1B6CA8; --blue-dark: #124E7C; --orange: #FF7A45; --orange-soft: #FFE8DC;
  --bg: #F7F9FC; --ink: #22303F; --ink-soft: #5A6B7C; --card: #FFFFFF;
  --green: #2FA36B; --radius: 18px; --shadow: 0 6px 24px rgba(27,108,168,.10);
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: "Source Han Sans SC","Noto Sans SC","Microsoft YaHei",system-ui,sans-serif;
  background: var(--bg); color: var(--ink); line-height: 1.8; font-size: 17px;
}

/* ---------- 顶部导航 ---------- */
.nav {
  position: sticky; top: 0; z-index: 50; background: rgba(255,255,255,.92);
  backdrop-filter: blur(8px); border-bottom: 1px solid #E6EDF4;
}
.nav-inner { max-width: 1080px; margin: 0 auto; padding: 12px 20px; display: flex; align-items: center; gap: 10px; }
.nav .logo { font-weight: 800; font-size: 19px; color: var(--blue); text-decoration: none; }
.nav .logo span { color: var(--orange); }
.nav .back { margin-left: auto; color: var(--ink-soft); text-decoration: none; font-size: 15px; }
.nav .back:hover { color: var(--blue); }

/* ---------- 版面 ---------- */
.wrap { max-width: 880px; margin: 0 auto; padding: 0 20px 80px; }
.hero { text-align: center; padding: 48px 0 24px; }
.hero .tag {
  display: inline-block; background: var(--orange-soft); color: var(--orange);
  font-size: 14px; font-weight: 700; padding: 4px 14px; border-radius: 99px; margin-bottom: 14px;
}
.hero h1 { font-size: 38px; line-height: 1.3; letter-spacing: 1px; }
.hero .sub { color: var(--ink-soft); font-size: 18px; margin-top: 12px; max-width: 640px; margin-inline: auto; }
.hero img { width: 100%; border-radius: 24px; margin-top: 28px; box-shadow: var(--shadow); }

/* ---------- 章节 ---------- */
section { margin-top: 64px; }
.sec-head { display: flex; align-items: center; gap: 14px; margin-bottom: 20px; }
.sec-num {
  flex: none; width: 44px; height: 44px; border-radius: 14px; background: var(--blue);
  color: #fff; font-weight: 800; font-size: 20px; display: grid; place-items: center;
  transform: rotate(-4deg);
}
.sec-head h2 { font-size: 26px; }
section p { margin: 14px 0; color: #34455A; }
section p b, section p strong { color: var(--blue-dark); }
.hi { background: linear-gradient(transparent 62%, #FFD9C7 62%); font-weight: 700; padding: 0 2px; }

/* ---------- 图片 & 热点标注 ---------- */
.figure { position: relative; border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow); background: #fff; }
.figure > img { display: block; width: 100%; }
.fig-cap { text-align: center; color: var(--ink-soft); font-size: 14.5px; margin-top: 10px; }
.hotspot {
  position: absolute; width: 30px; height: 30px; border-radius: 50%; border: none;
  background: var(--orange); color: #fff; font-weight: 800; cursor: pointer;
  box-shadow: 0 0 0 5px rgba(255,122,69,.28); animation: pulse 2s infinite;
  transition: transform .15s;
}
.hotspot:hover { transform: scale(1.18); }
@keyframes pulse { 50% { box-shadow: 0 0 0 10px rgba(255,122,69,0); } }
.tip {
  position: absolute; z-index: 10; width: 240px; background: #fff; border-radius: 14px;
  box-shadow: 0 10px 30px rgba(34,48,63,.18); padding: 12px 14px; font-size: 14.5px; line-height: 1.6;
  opacity: 0; pointer-events: none; transform: translateY(6px); transition: .2s;
}
.tip.show { opacity: 1; transform: translateY(0); pointer-events: auto; }
.tip b { color: var(--blue); display: block; margin-bottom: 2px; }

/* ---------- 卡片们 ---------- */
.card { background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow); padding: 26px 28px; }
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; }
@media (max-width: 640px) { .grid2 { grid-template-columns: 1fr; } .hero h1 { font-size: 30px; } }

/* 比喻实验卡 */
.lab { border-left: 6px solid var(--orange); background: #FFF9F5; border-radius: 0 var(--radius) var(--radius) 0; padding: 20px 24px; margin: 22px 0; }
.lab .lab-title { font-weight: 800; color: var(--orange); margin-bottom: 6px; }

/* 动力流程链 */
.flow { display: flex; align-items: stretch; gap: 0; margin: 24px 0; flex-wrap: wrap; }
.flow .step {
  flex: 1; min-width: 130px; background: #fff; border: 2px solid #DCE7F1; border-radius: 16px;
  padding: 16px 14px; text-align: center; position: relative;
}
.flow .step .ico { font-size: 30px; }
.flow .step b { display: block; margin: 6px 0 2px; color: var(--blue-dark); }
.flow .step small { color: var(--ink-soft); line-height: 1.5; display: block; }
.flow .arrow { align-self: center; color: var(--orange); font-size: 24px; font-weight: 800; padding: 0 8px; }

/* 冷知识 */
.facts { display: grid; gap: 14px; }
.fact { background: #fff; border-radius: 14px; padding: 16px 20px; display: flex; gap: 14px; box-shadow: var(--shadow); }
.fact .bulb { flex: none; font-size: 24px; }

/* 考考你 */
.quiz { background: #fff; border-radius: var(--radius); box-shadow: var(--shadow); padding: 24px 28px; margin-bottom: 18px; }
.quiz .q { font-weight: 700; margin-bottom: 12px; }
.quiz .opts { display: grid; gap: 10px; }
.quiz button {
  text-align: left; padding: 12px 16px; border-radius: 12px; border: 2px solid #DCE7F1;
  background: #FBFDFF; font-size: 15.5px; cursor: pointer; font-family: inherit; transition: .15s;
}
.quiz button:hover { border-color: var(--blue); }
.quiz button.right { border-color: var(--green); background: #EAF7F0; }
.quiz button.wrong { border-color: #E25C5C; background: #FDECEC; }
.quiz .why { display: none; margin-top: 12px; font-size: 15px; color: var(--ink-soft); background: #F2F7FB; border-radius: 10px; padding: 10px 14px; }
.quiz.done .why { display: block; }

/* 滚动渐现 */
.reveal { opacity: 0; transform: translateY(24px); transition: .7s ease; }
.reveal.in { opacity: 1; transform: none; }

/* 页脚 */
footer { text-align: center; color: var(--ink-soft); font-size: 14px; padding: 36px 0 20px; }

/* ---------- 首页卡片墙 ---------- */
.home-grid { display: grid; grid-template-columns: repeat(auto-fill,minmax(240px,1fr)); gap: 20px; margin-top: 30px; }
.topic-card {
  background: #fff; border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow);
  text-decoration: none; color: inherit; transition: transform .2s;
}
.topic-card:hover { transform: translateY(-5px); }
.topic-card img { width: 100%; aspect-ratio: 1; object-fit: cover; }
.topic-card .tc-body { padding: 16px 18px; }
.topic-card h3 { font-size: 18px; }
.topic-card p { font-size: 14px; color: var(--ink-soft); margin-top: 4px; line-height: 1.6; }
.topic-card .soon { display: inline-block; font-size: 12px; background: #EDF2F7; color: var(--ink-soft); border-radius: 99px; padding: 2px 10px; margin-top: 8px; }