:root {
  color-scheme: dark;
  font-family: Inter, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei",
    ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;

  --bg: #0a0a0a;
  --bg-soft: #111;
  --fg: #f5f5f5;
  --fg-dim: #a3a3a3;
  --fg-faint: #525252;
  --line: rgba(255, 255, 255, 0.08);
  --line-strong: rgba(255, 255, 255, 0.16);

  --grad: linear-gradient(90deg, #ff0080, #ff8c00, #40e0d0, #8b5cf6, #ff0080);

  --max-w: 1100px;
  --pad-x: clamp(1.25rem, 4vw, 3rem);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100svh;
  background: var(--bg);
  color: var(--fg);
  font-size: 17px;
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
}

/* ---------- language toggle (data-lang on body controls visibility) ---------- */
body[data-lang="zh"] .en { display: none; }
body[data-lang="en"] .zh { display: none; }

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

a:hover {
  color: #fff;
}

/* ---------- header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem var(--pad-x);
  background: rgba(10, 10, 10, 0.7);
  backdrop-filter: saturate(140%) blur(12px);
  -webkit-backdrop-filter: saturate(140%) blur(12px);
  border-bottom: 1px solid var(--line);
}

.brand {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
  display: inline-flex;
  align-items: baseline;
}

.brand-future {
  background: var(--grad);
  background-size: 300% 100%;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  animation: shimmer 6s ease-in-out infinite;
}

.brand-dev {
  color: var(--fg);
}

.lang-toggle {
  appearance: none;
  background: transparent;
  border: 1px solid var(--line-strong);
  color: var(--fg-dim);
  font: inherit;
  font-size: 0.85rem;
  padding: 0.4rem 0.7rem;
  border-radius: 999px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  transition: border-color 0.15s ease, color 0.15s ease;
}

.lang-toggle:hover {
  border-color: var(--fg-dim);
  color: var(--fg);
}

.lang-opt {
  padding: 0 0.1rem;
  transition: color 0.15s ease;
}

.lang-sep {
  color: var(--fg-faint);
}

body[data-lang="zh"] .lang-opt[data-lang-target="zh"],
body[data-lang="en"] .lang-opt[data-lang-target="en"] {
  color: var(--fg);
  font-weight: 600;
}

/* ---------- shared section ---------- */
main {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 var(--pad-x);
}

section {
  padding: clamp(4rem, 10vw, 7rem) 0;
  border-bottom: 1px solid var(--line);
}

section:last-of-type {
  border-bottom: none;
}

.section-title {
  font-size: clamp(1.6rem, 3.5vw, 2.4rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 0 0 2.5rem;
  line-height: 1.15;
}

/* ---------- hero ---------- */
.hero {
  padding-top: clamp(5rem, 12vw, 9rem);
  padding-bottom: clamp(5rem, 12vw, 9rem);
  border-bottom: 1px solid var(--line);
  text-align: left;
}

.hero-title {
  margin: 0 0 1.5rem;
  font-size: clamp(3rem, 11vw, 8.5rem);
  font-weight: 800;
  line-height: 0.95;
  letter-spacing: -0.04em;
  background: var(--grad);
  background-size: 300% 100%;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  animation: shimmer 4s ease-in-out infinite;
}

.hero-sub {
  font-size: clamp(1.1rem, 2.2vw, 1.45rem);
  color: var(--fg-dim);
  max-width: 36ch;
  margin: 0 0 2.5rem;
  line-height: 1.4;
}

.hero-cta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  padding: 0.85rem 1.4rem;
  border-radius: 999px;
  font-weight: 600;
  font-size: 0.95rem;
  transition: transform 0.15s ease, background 0.15s ease, color 0.15s ease,
    border-color 0.15s ease;
}

.btn:hover {
  transform: translateY(-1px);
}

.btn-primary {
  background: var(--fg);
  color: var(--bg);
}

.btn-primary:hover {
  background: #fff;
  color: var(--bg);
}

.btn-ghost {
  border: 1px solid var(--line-strong);
  color: var(--fg);
}

.btn-ghost:hover {
  border-color: var(--fg-dim);
  color: #fff;
}

/* ---------- vibe ---------- */
.vibe-body {
  display: grid;
  gap: 1.25rem;
  max-width: 60ch;
  font-size: clamp(1.05rem, 1.6vw, 1.2rem);
  color: var(--fg-dim);
}

.vibe-body p {
  margin: 0;
}

.vibe-body p:first-child {
  color: var(--fg);
}

/* ---------- why (cards) ---------- */
.cards {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 1rem;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}

.card {
  position: relative;
  padding: 1.75rem 1.5rem 1.5rem;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.025), transparent);
  transition: border-color 0.2s ease, transform 0.2s ease;
}

.card:hover {
  border-color: var(--line-strong);
  transform: translateY(-2px);
}

.card-num {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.8rem;
  color: var(--fg-faint);
  margin-bottom: 0.85rem;
  letter-spacing: 0.05em;
}

.card h3 {
  margin: 0 0 0.6rem;
  font-size: 1.1rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.card p {
  margin: 0;
  color: var(--fg-dim);
  font-size: 0.95rem;
  line-height: 1.5;
}

/* ---------- curriculum ---------- */
.modules {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0;
}

.module {
  display: grid;
  grid-template-columns: 5rem 1fr;
  gap: 1.5rem;
  padding: 1.75rem 0;
  border-top: 1px solid var(--line);
  align-items: baseline;
}

.module:last-child {
  border-bottom: 1px solid var(--line);
}

.module-tag {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 1rem;
  color: var(--fg-faint);
  letter-spacing: 0.05em;
  padding-top: 0.15rem;
}

.module-body h3 {
  margin: 0 0 0.45rem;
  font-size: clamp(1.15rem, 2vw, 1.35rem);
  font-weight: 600;
  letter-spacing: -0.01em;
  background: var(--grad);
  background-size: 300% 100%;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.module-body p {
  margin: 0;
  color: var(--fg-dim);
  max-width: 56ch;
}

/* ---------- join ---------- */
.join-grid {
  display: grid;
  gap: 1.25rem;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}

.join-item {
  padding: 1.5rem;
  border: 1px solid var(--line);
  border-radius: 18px;
}

.join-label {
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-size: 0.8rem;
  color: var(--fg-faint);
  letter-spacing: 0.05em;
  margin-bottom: 0.65rem;
  text-transform: uppercase;
}

.join-value {
  color: var(--fg);
  font-size: 1.02rem;
}

.join-value a {
  border-bottom: 1px solid var(--line-strong);
  padding-bottom: 1px;
  transition: border-color 0.15s ease;
}

.join-value a:hover {
  border-color: #fff;
}

/* ---------- footer ---------- */
.site-footer {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 2rem var(--pad-x) 3rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  color: var(--fg-faint);
  font-size: 0.85rem;
  border-top: 1px solid var(--line);
  flex-wrap: wrap;
}

.footer-link {
  color: var(--fg-dim);
}

.footer-link:hover {
  color: var(--fg);
}

.footer-arrow {
  display: inline-block;
  transition: transform 0.15s ease;
}

.footer-link:hover .footer-arrow {
  transform: translateX(-3px);
}

/* ---------- animation ---------- */
@keyframes shimmer {
  0%   { background-position: 0% 50%; }
  50%  { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}

@media (prefers-reduced-motion: reduce) {
  .hero-title,
  .brand-future,
  .module-body h3 {
    animation: none;
  }
  html { scroll-behavior: auto; }
  .btn:hover,
  .card:hover,
  .footer-link:hover .footer-arrow { transform: none; }
}

/* ---------- small screens ---------- */
@media (max-width: 560px) {
  .module {
    grid-template-columns: 1fr;
    gap: 0.4rem;
  }
  .site-footer {
    justify-content: flex-start;
  }
}