:root {
  color-scheme: light;
  --ink: #16202a;
  --muted: #5d6d78;
  --paper: #f6f9fa;
  --panel: #ffffff;
  --line: #d7e1e6;
  --deep: #102230;
  --steel: #2d5a78;
  --water: #0a8d93;
  --heat: #bd5232;
  --amber: #dfa13a;
  --soft: #edf4f6;
  --shadow: 0 18px 44px rgba(31, 55, 70, 0.12);
  font-family: "Inter", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  line-height: 1.68;
}

a {
  color: var(--steel);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 18px;
  min-height: 62px;
  padding: 0 28px;
  border-bottom: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.94);
  backdrop-filter: blur(14px);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--deep);
  font-weight: 900;
}

.brand-mark {
  width: 28px;
  height: 28px;
  border-radius: 7px;
  background: linear-gradient(135deg, var(--heat), var(--amber) 45%, var(--water) 46%, var(--steel));
}

.topbar nav {
  display: flex;
  gap: 4px;
  overflow-x: auto;
  white-space: nowrap;
}

.topbar nav a {
  min-height: 36px;
  padding: 7px 11px;
  border-radius: 6px;
  color: #415464;
  font-size: 14px;
  font-weight: 800;
}

.topbar nav a:hover {
  background: var(--soft);
  text-decoration: none;
}

.hero {
  color: #fff;
  background:
    linear-gradient(90deg, rgba(12, 26, 37, 0.90), rgba(12, 26, 37, 0.58)),
    var(--hero-image) center / cover no-repeat,
    #142635;
}

.hero-inner,
.wrap {
  width: min(1120px, calc(100% - 48px));
  margin: 0 auto;
}

.hero-inner {
  min-height: 520px;
  display: grid;
  grid-template-columns: minmax(0, 0.72fr) minmax(320px, 0.28fr);
  gap: 38px;
  align-items: center;
  padding: 72px 0;
}

.eyebrow {
  margin: 0 0 14px;
  color: #bde8e9;
  font-size: 14px;
  font-weight: 900;
}

h1,
h2,
h3,
p,
li,
td,
th {
  overflow-wrap: anywhere;
}

h1 {
  margin: 0;
  max-width: 780px;
  font-size: 52px;
  line-height: 1.08;
  letter-spacing: 0;
}

.hero-copy {
  max-width: 760px;
  margin: 22px 0 0;
  color: #e3edf0;
  font-size: 18px;
  font-weight: 650;
}

.lesson-meta {
  display: grid;
  gap: 10px;
  padding: 20px;
  border: 1px solid rgba(255, 255, 255, 0.22);
  border-radius: 8px;
  background: rgba(14, 31, 44, 0.78);
  box-shadow: 0 22px 60px rgba(0, 0, 0, 0.26);
}

.meta-item {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  padding: 11px 0;
  border-bottom: 1px solid rgba(255, 255, 255, 0.14);
  color: #c8dce2;
  font-weight: 800;
}

.meta-item:last-child {
  border-bottom: 0;
}

.meta-item b {
  color: #fff;
}

section {
  padding: 66px 0;
}

.section-dark {
  color: #fff;
  background: var(--deep);
}

.section-white {
  background: #fff;
}

.section-muted {
  background: #eef4f6;
}

.section-head {
  display: grid;
  grid-template-columns: minmax(0, 0.72fr) minmax(280px, 0.28fr);
  gap: 30px;
  align-items: end;
  margin-bottom: 28px;
}

.kicker {
  margin: 0 0 9px;
  color: var(--water);
  font-size: 13px;
  font-weight: 900;
}

.section-dark .kicker {
  color: #8ee1df;
}

h2 {
  margin: 0;
  font-size: 34px;
  line-height: 1.18;
}

.section-dark h2 {
  color: #fff;
}

.lead {
  margin: 0;
  color: var(--muted);
  font-weight: 650;
}

.section-dark .lead {
  color: #bed3da;
}

.objective {
  padding: 24px;
  border-left: 5px solid var(--amber);
  border-radius: 8px;
  background: #fff;
  box-shadow: var(--shadow);
  font-size: 20px;
  font-weight: 850;
}

.visual-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(320px, 0.52fr);
  gap: 22px;
  align-items: stretch;
}

.visual-card,
.note-card,
.quiz-card,
.link-card {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  box-shadow: 0 10px 28px rgba(31, 55, 70, 0.08);
  overflow: hidden;
}

.visual-card img {
  width: 100%;
  height: 100%;
  min-height: 360px;
  object-fit: cover;
  display: block;
}

.note-card {
  padding: 22px;
}

.note-card h3,
.quiz-card h3,
.link-card h3 {
  margin: 0 0 12px;
  font-size: 21px;
  line-height: 1.28;
}

.note-card ul,
.quiz-card ol,
.link-card ul {
  display: grid;
  gap: 10px;
  margin: 0;
  padding-left: 20px;
}

.note-card li,
.quiz-card li,
.link-card li {
  color: #415461;
  font-weight: 650;
}

.two-col {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.metric-table {
  overflow: auto;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  box-shadow: var(--shadow);
}

table {
  width: 100%;
  min-width: 680px;
  border-collapse: collapse;
  color: var(--ink);
}

th,
td {
  color: #344b5a;
}

td {
  padding: 14px 16px;
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

th {
  color: #244358;
  background: #edf4f7;
  font-weight: 900;
}

tr:last-child td {
  border-bottom: 0;
}

.quiz-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 16px;
}

.quiz-card {
  min-height: 210px;
  padding: 20px;
}

details {
  margin-top: 14px;
  color: var(--muted);
  font-weight: 700;
}

summary {
  cursor: pointer;
  color: var(--steel);
  font-weight: 900;
}

.link-card {
  padding: 22px;
}

.tech-read-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.tech-read-card {
  display: flex;
  flex-direction: column;
  min-height: 310px;
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  box-shadow: 0 10px 28px rgba(31, 55, 70, 0.08);
}

.tech-read-card b {
  display: inline-flex;
  align-self: flex-start;
  min-height: 26px;
  padding: 2px 9px;
  border-radius: 999px;
  color: var(--deep);
  background: #fbf0da;
  font-size: 12px;
}

.tech-read-card h3 {
  margin: 13px 0 9px;
  font-size: 21px;
  line-height: 1.28;
}

.tech-read-card p {
  margin: 0;
  color: var(--muted);
  font-weight: 650;
}

.tech-read-card ul {
  display: grid;
  gap: 8px;
  margin: 14px 0 0;
  padding-left: 18px;
}

.tech-read-card li {
  color: #415461;
  font-size: 14px;
  font-weight: 650;
}

.tech-read-card .button {
  align-self: flex-start;
  margin-top: auto;
}

.next-row {
  display: flex;
  justify-content: space-between;
  gap: 14px;
  padding: 28px 0 50px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 42px;
  padding: 0 15px;
  border: 1px solid var(--line);
  border-radius: 6px;
  color: var(--deep);
  background: #fff;
  font-weight: 900;
}

.button.primary {
  border-color: var(--amber);
  background: #f4bd5d;
}

.button:hover {
  text-decoration: none;
  filter: brightness(0.98);
}

@media (max-width: 900px) {
  .topbar {
    align-items: flex-start;
    flex-direction: column;
    padding: 12px 18px;
  }

  .hero-inner,
  .section-head,
  .visual-grid,
  .two-col,
  .quiz-grid,
  .tech-read-grid {
    grid-template-columns: 1fr;
  }

  h1 {
    font-size: 38px;
  }

  h2 {
    font-size: 28px;
  }

  .hero-inner,
  .wrap {
    width: min(100% - 28px, 720px);
  }

  .hero-inner {
    min-height: auto;
    padding: 54px 0 42px;
  }

  section {
    padding: 52px 0;
  }

  .visual-card img {
    min-height: 260px;
  }
}

@media (max-width: 560px) {
  h1 {
    font-size: 32px;
  }

  .hero-copy {
    font-size: 16px;
  }

  .next-row {
    align-items: stretch;
    flex-direction: column;
  }
}