:root {
  --background: #eef7f8;
  --foreground: #07151b;
  --panel: rgba(255, 255, 255, 0.88);
  --panel-strong: #ffffff;
  --line: #c9dfe4;
  --cyan: #21c8d8;
  --teal: #0d6874;
  --orange: #ff823c;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background:
    linear-gradient(rgba(19, 117, 132, 0.06) 1px, transparent 1px),
    linear-gradient(90deg, rgba(19, 117, 132, 0.06) 1px, transparent 1px),
    radial-gradient(circle at 88% 8%, rgba(33, 200, 216, 0.24), transparent 28%),
    linear-gradient(135deg, #f8fcfd 0%, #edf7f8 58%, #dff0f3 100%);
  background-size: 64px 64px, 64px 64px, auto, auto;
  color: var(--foreground);
  font-family: "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", Arial, sans-serif;
}

button,
a {
  font: inherit;
}

button {
  border: 0;
}

main {
  min-height: 100vh;
}

.hero {
  min-height: 92vh;
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(320px, 0.95fr);
  gap: 52px;
  align-items: center;
  width: min(1180px, calc(100% - 40px));
  margin: 0 auto;
  padding: 70px 0 46px;
}

.heroText {
  min-width: 0;
}

.eyebrow,
.sectionKicker {
  margin: 0 0 14px;
  color: var(--teal);
  font-size: 14px;
  font-weight: 900;
  letter-spacing: 0.18em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 24px;
  font-size: clamp(48px, 7vw, 92px);
  line-height: 0.98;
  font-weight: 950;
  letter-spacing: 0;
}

.heroLead {
  max-width: 690px;
  color: #263941;
  font-size: 22px;
  line-height: 1.65;
  font-weight: 650;
}

.heroStats {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 34px;
}

.heroStats span {
  min-width: 132px;
  padding: 14px 18px;
  background: var(--panel-strong);
  border-top: 4px solid var(--cyan);
  box-shadow: 0 18px 44px rgba(15, 70, 82, 0.1);
  font-size: 18px;
  font-weight: 900;
}

.heroImage {
  position: relative;
  padding: 34px;
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--line);
  box-shadow: 0 28px 70px rgba(15, 70, 82, 0.14);
}

.heroImage::before {
  content: "";
  position: absolute;
  inset: 18px;
  border: 1px solid rgba(13, 104, 116, 0.14);
  pointer-events: none;
}

.heroImage img {
  position: relative;
  width: 100%;
  display: block;
}

.topicNav {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  gap: 10px;
  overflow-x: auto;
  width: min(1180px, calc(100% - 24px));
  margin: 0 auto 42px;
  padding: 12px;
  background: rgba(255, 255, 255, 0.9);
  border: 1px solid var(--line);
  backdrop-filter: blur(14px);
  box-shadow: 0 16px 34px rgba(15, 70, 82, 0.08);
}

.topicNav a {
  flex: 0 0 auto;
  padding: 12px 16px;
  color: #07151b;
  text-decoration: none;
  background: #e9f6f8;
  border-left: 4px solid var(--cyan);
  font-weight: 900;
}

.topicSection {
  width: min(1180px, calc(100% - 40px));
  margin: 0 auto 54px;
}

h2 {
  margin-bottom: 14px;
  font-size: 42px;
  line-height: 1.08;
  font-weight: 950;
}

.topicHeader p {
  color: #30464d;
  font-size: 18px;
  line-height: 1.7;
  font-weight: 650;
}

.topicSection {
  scroll-margin-top: 100px;
  padding: 34px;
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid var(--line);
  box-shadow: 0 22px 56px rgba(15, 70, 82, 0.1);
}

.topicHeader {
  display: grid;
  grid-template-columns: 82px 1fr;
  gap: 24px;
  align-items: start;
  margin-bottom: 26px;
}

.topicHeader > span {
  display: grid;
  place-items: center;
  width: 72px;
  height: 72px;
  background: #ffffff;
  border: 3px solid var(--cyan);
  border-radius: 50%;
  font-size: 30px;
  font-weight: 950;
}

.topicImage {
  margin-bottom: 26px;
  padding: 24px;
  background: #ffffff;
  border: 1px solid var(--line);
}

.topicImage img {
  display: block;
  width: 100%;
  max-height: 430px;
  object-fit: contain;
}

.learningGrid {
  display: grid;
  grid-template-columns: minmax(0, 0.95fr) minmax(0, 1.05fr);
  gap: 24px;
}

.panel {
  min-width: 0;
  padding: 24px;
  background: var(--panel-strong);
  border: 1px solid var(--line);
}

.panel h3 {
  margin-bottom: 20px;
  font-size: 28px;
  line-height: 1.1;
  font-weight: 950;
}

.termList,
.sentenceList {
  display: grid;
  gap: 12px;
}

.termItem,
.sentenceItem {
  padding: 16px;
  background: #f4fbfc;
  border-left: 5px solid var(--cyan);
}

.termItem {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 16px;
  align-items: center;
}

.zh {
  margin-bottom: 6px;
  font-size: 18px;
  font-weight: 900;
}

.en,
.sentenceEn {
  margin-bottom: 6px;
  color: #07151b;
  font-size: 22px;
  line-height: 1.28;
  font-weight: 950;
}

.note,
.sentenceZh {
  margin-bottom: 0;
  color: #3d5158;
  font-size: 15px;
  line-height: 1.5;
  font-weight: 650;
}

.termItem button,
.sentenceTop button {
  min-width: 66px;
  padding: 10px 14px;
  color: #07151b;
  background: #ffffff;
  border: 2px solid var(--cyan);
  font-size: 15px;
  font-weight: 950;
  cursor: pointer;
}

.termItem button:hover,
.sentenceTop button:hover {
  background: #d9f7fa;
}

.sentenceTop {
  display: flex;
  gap: 12px;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}

.sentenceTop span {
  color: var(--teal);
  font-size: 15px;
  font-weight: 950;
  letter-spacing: 0.08em;
}

@media (max-width: 860px) {
  .hero,
  .learningGrid {
    grid-template-columns: 1fr;
  }

  .hero {
    min-height: auto;
    padding-top: 36px;
  }

  h1 {
    font-size: 48px;
  }

  h2 {
    font-size: 34px;
  }

  .topicHeader {
    grid-template-columns: 1fr;
    gap: 16px;
  }

  .topicSection {
    width: min(100% - 24px, 1180px);
    padding: 22px;
  }

  .termItem {
    grid-template-columns: 1fr;
  }
}