:root {
  --green: #7C9473;
  --brown: #A86F4D;
  --sand: #B5A273;
  --apricot: #E3C9A7;
  --sage: #6E8E82;
  --text: #4A4A43;
  --text-light: #7A7A70;
  --bg: #F5F2E9;
  --white: #FFFDF8;
  --shadow-sm: 0 2px 8px rgba(74, 74, 67, 0.06);
  --shadow-md: 0 4px 16px rgba(74, 74, 67, 0.08);
  --radius: 16px;
  --font: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
}

body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
  min-height: 100vh;
}

a {
  text-decoration: none;
  color: inherit;
}

/* ---------- Hero ---------- */
.hero {
  text-align: center;
  padding: 3rem 1.5rem 2.5rem;
  background: radial-gradient(ellipse 80% 60% at 50% 30%, rgba(124, 148, 115, 0.08) 0%, transparent 60%), var(--bg);
}

.hero-nav {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin-bottom: 2rem;
  font-size: 0.85rem;
  color: var(--sage);
}

.hero-nav a {
  color: var(--sage);
  transition: color var(--transition);
}

.hero-nav a:hover {
  color: var(--green);
}

.hero-nav span {
  color: var(--text-light);
}

.hero-inner {
  max-width: 640px;
  margin: 0 auto;
}

.hero-inner h1 {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  font-weight: 700;
  color: var(--text);
  letter-spacing: 0.02em;
}

.hero-sub {
  font-size: 0.9rem;
  color: var(--text-light);
  letter-spacing: 0.06em;
  margin: 0.25rem 0 0.75rem;
}

.hero-desc {
  font-size: 0.95rem;
  color: var(--text-light);
  line-height: 1.8;
}

/* ---------- Module Grid ---------- */
.modules {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 1.5rem 4rem;
}

.section-title {
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--text);
  text-align: center;
  margin-bottom: 1.5rem;
}

.module-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.25rem;
}

.module-card {
  display: flex;
  flex-direction: column;
  background: var(--white);
  border-radius: var(--radius);
  padding: 1.5rem;
  border: 1px solid rgba(74, 74, 67, 0.06);
  border-left: 3px solid var(--green);
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition);
  cursor: pointer;
}

.module-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  border-color: rgba(124, 148, 115, 0.25);
}

.module-icon {
  font-size: 2rem;
  line-height: 1;
  margin-bottom: 0.5rem;
}

.module-card h3 {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.3rem;
}

.module-meta {
  font-size: 0.8rem;
  color: var(--sand);
  margin-bottom: 0.5rem;
}

.module-card p {
  font-size: 0.85rem;
  color: var(--text-light);
  line-height: 1.6;
  flex: 1;
}

/* ---------- Activity Content ---------- */
.content {
  max-width: 760px;
  margin: 0 auto;
  padding: 0 1.5rem 4rem;
}

.activity {
  background: var(--white);
  border-radius: var(--radius);
  padding: 1.75rem;
  margin-bottom: 1.5rem;
  border: 1px solid rgba(74, 74, 67, 0.06);
  border-left: 3px solid var(--green);
  box-shadow: var(--shadow-sm);
}

.activity-header {
  display: flex;
  align-items: baseline;
  gap: 0.75rem;
  margin-bottom: 0.75rem;
}

.activity-number {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--green);
  background: rgba(124, 148, 115, 0.1);
  padding: 0.15em 0.6em;
  border-radius: 999px;
  white-space: nowrap;
}

.activity h3 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--text);
}

.ngss-tag {
  font-size: 0.7rem;
  color: var(--sand);
  background: rgba(181, 162, 115, 0.1);
  padding: 0.15em 0.6em;
  border-radius: 999px;
  margin-bottom: 0.75rem;
  display: inline-block;
}

.activity-section {
  margin-bottom: 0.75rem;
}

.activity-section h4 {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--brown);
  margin-bottom: 0.25rem;
}

.activity-section p,
.activity-section li {
  font-size: 0.85rem;
  color: var(--text-light);
  line-height: 1.7;
}

.activity-section ul {
  padding-left: 1.25rem;
}

.vocab-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.5rem;
}

.vocab-item {
  font-size: 0.78rem;
  color: var(--text);
  background: rgba(124, 148, 115, 0.06);
  padding: 0.2em 0.65em;
  border-radius: 999px;
  border: 1px solid rgba(124, 148, 115, 0.15);
}

.equation {
  font-family: "Courier New", monospace;
  font-size: 0.9rem;
  color: var(--text);
  background: rgba(124, 148, 115, 0.06);
  padding: 0.5rem 1rem;
  border-radius: 8px;
  display: inline-block;
  margin: 0.5rem 0;
}

/* ---------- Standards Footer ---------- */
.standards {
  background: var(--white);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-top: 2rem;
  border: 1px solid rgba(74, 74, 67, 0.06);
}

.standards h4 {
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.5rem;
}

.standards ul {
  padding-left: 1.25rem;
  font-size: 0.82rem;
  color: var(--text-light);
  line-height: 1.8;
}

/* ---------- Site Footer ---------- */
.site-footer {
  text-align: center;
  padding: 2rem 1.5rem;
  border-top: 1px solid rgba(74, 74, 67, 0.08);
}

.site-footer a {
  font-size: 0.85rem;
  color: var(--text-light);
  transition: color var(--transition);
}

.site-footer a:hover {
  color: var(--green);
}

@media (max-width: 768px) {
  .module-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 480px) {
  .hero {
    padding: 2rem 1rem 1.5rem;
  }
  .activity {
    padding: 1.25rem;
  }
}