:root {
  --ink: #10243d;
  --ink-soft: #3b5a78;
  --paper: #fdfcf9;
  --card: #ffffffdd;
  --line: #d7e1eb;
  --brand: #e86a33;
  --accent: #2a9d8f;
  --shadow: 0 14px 40px rgba(16, 36, 61, 0.12);
  --radius: 18px;
  --font-ui: "Noto Sans SC", "Source Han Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-head: "HarmonyOS Sans SC", "Noto Serif SC", "Source Han Serif SC", serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  min-height: 100%;
}

body {
  font-family: var(--font-ui);
  color: var(--ink);
  background:
    radial-gradient(circle at 15% 10%, #ffd9b8 0 22%, transparent 23%),
    radial-gradient(circle at 90% 5%, #cbf1ea 0 18%, transparent 19%),
    linear-gradient(160deg, #f2f7fb 0%, #f6f1e9 48%, #fffaf2 100%);
  overflow-x: hidden;
}

.bg-shape {
  position: fixed;
  border-radius: 999px;
  filter: blur(50px);
  z-index: -1;
  opacity: 0.25;
}

.bg-shape-1 {
  width: 280px;
  height: 280px;
  top: -60px;
  right: -70px;
  background: #3da5d9;
}

.bg-shape-2 {
  width: 240px;
  height: 240px;
  bottom: -60px;
  left: -30px;
  background: #f4a261;
}

.app-header {
  padding: 24px 18px 14px;
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
  align-items: end;
  justify-content: space-between;
}

.title-wrap h1 {
  margin: 4px 0;
  font-family: var(--font-head);
  font-size: clamp(1.5rem, 4vw, 2.2rem);
  letter-spacing: 0.4px;
}

.eyebrow {
  margin: 0;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: #6f879e;
}

.subtext {
  margin: 0;
  color: var(--ink-soft);
  font-size: 0.94rem;
}

.search-box {
  display: grid;
  gap: 6px;
  font-size: 0.88rem;
  color: var(--ink-soft);
}

.search-box input {
  width: min(90vw, 430px);
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fff;
  padding: 11px 12px;
  font-size: 0.95rem;
  color: var(--ink);
}

.search-box input:focus {
  outline: 2px solid #9dd4ce;
  border-color: transparent;
}

.layout {
  display: grid;
  grid-template-columns: minmax(260px, 340px) minmax(0, 1fr);
  gap: 14px;
  padding: 0 14px 14px;
}

.lesson-nav,
.content-panel {
  background: var(--card);
  backdrop-filter: blur(6px);
  border: 1px solid #ffffffaa;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.lesson-nav {
  min-height: 72vh;
  overflow: hidden;
  display: grid;
  grid-template-rows: auto 1fr;
}

.nav-head {
  padding: 14px 14px 10px;
  border-bottom: 1px solid var(--line);
}

.nav-head h2 {
  margin: 0;
  font-size: 1.02rem;
}

.nav-head p {
  margin: 4px 0 0;
  font-size: 0.86rem;
  color: var(--ink-soft);
}

.lesson-list {
  list-style: none;
  margin: 0;
  padding: 10px;
  overflow: auto;
  display: grid;
  gap: 8px;
}

.lesson-item button {
  width: 100%;
  text-align: left;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fff;
  padding: 11px 12px;
  color: var(--ink);
  font-size: 0.92rem;
  line-height: 1.35;
  cursor: pointer;
  transition: transform 130ms ease, border-color 130ms ease, box-shadow 130ms ease;
}

.lesson-item button:hover {
  transform: translateY(-1px);
  border-color: #9fc2dd;
  box-shadow: 0 8px 16px rgba(50, 80, 110, 0.1);
}

.lesson-item.active button {
  border-color: var(--accent);
  background: linear-gradient(120deg, #f1f9f8, #fbfffe);
}

.content-panel {
  min-height: 72vh;
  overflow: auto;
}

.lesson-detail {
  padding: 18px;
  animation: riseIn 180ms ease;
}

.placeholder {
  color: var(--ink-soft);
}

.detail-title {
  margin: 0 0 4px;
  font-family: var(--font-head);
  font-size: clamp(1.28rem, 3vw, 1.76rem);
}

.detail-meta {
  margin: 0 0 14px;
  font-size: 0.9rem;
  color: var(--ink-soft);
}

.section-card {
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 12px 13px;
  margin: 10px 0;
  background: #fff;
}

.section-card h3 {
  margin: 0 0 8px;
  color: #21486d;
  font-size: 1.03rem;
}

.section-card h4 {
  margin: 11px 0 6px;
  color: #325d83;
  font-size: 0.96rem;
}

.section-card p,
.section-card li,
.section-card blockquote {
  line-height: 1.62;
}

.section-card ul {
  margin: 6px 0 8px 20px;
  padding: 0;
}

.section-card table {
  width: 100%;
  border-collapse: collapse;
  margin: 8px 0;
}

.section-card th,
.section-card td {
  border: 1px solid var(--line);
  padding: 8px 7px;
  vertical-align: top;
  font-size: 0.91rem;
}

.section-card th {
  background: #f4f8fb;
}

.section-card blockquote {
  margin: 8px 0;
  border-left: 3px solid #9dc4df;
  padding: 6px 10px;
  color: #3a5976;
  background: #f9fcff;
}

.section-card code {
  background: #f0f4f8;
  border-radius: 4px;
  padding: 2px 5px;
  font-size: 0.88em;
}

.kw-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 8px;
}

.kw-item {
  border: 1px dashed #b9d3e7;
  border-radius: 10px;
  padding: 9px 10px;
  background: linear-gradient(110deg, #fcfffe, #f9fcff);
}

.kw-item strong {
  color: #20496d;
}

.media-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.media-links a {
  color: #245f8f;
  text-decoration: none;
  border: 1px solid #bcd5e7;
  border-radius: 999px;
  padding: 6px 10px;
  font-size: 0.87rem;
  background: #fff;
}

.media-links a:hover {
  border-color: #8fb6d1;
}

mark {
  background: #ffe8b5;
  color: inherit;
  border-radius: 2px;
}

.app-footer {
  text-align: center;
  padding: 6px 12px 18px;
  color: #6f8398;
  font-size: 0.8rem;
}

@keyframes riseIn {
  from {
    opacity: 0;
    transform: translateY(4px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (max-width: 900px) {
  .layout {
    grid-template-columns: 1fr;
  }

  .lesson-nav {
    min-height: 40vh;
  }

  .content-panel {
    min-height: 50vh;
  }
}