/* ===========================================================
   ViavaCos — self-contained styles
   No frameworks, no external fonts. Edit the variables below
   to re-skin the whole site.
   =========================================================== */

:root {
  --bg: #ffffff;
  --bg-soft: #f5f6f8;
  --bg-elev: #ffffff;
  --text: #1a1d24;
  --text-soft: #5b6472;
  --border: #e6e8ec;
  --accent: #6c5ce7;
  --accent-2: #00b8d4;
  --shadow: 0 8px 30px rgba(20, 23, 33, 0.08);
  --radius: 14px;
  --maxw: 980px;
  --nav-h: 62px;
  color-scheme: light;
}

[data-theme="dark"] {
  --bg: #0f1115;
  --bg-soft: #161a21;
  --bg-elev: #1b2029;
  --text: #e7eaf0;
  --text-soft: #9aa4b2;
  --border: #2a313c;
  --accent: #a29bfe;
  --accent-2: #4dd0e1;
  --shadow: 0 8px 30px rgba(0, 0, 0, 0.45);
  color-scheme: dark;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, "PingFang SC", "Microsoft YaHei", sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  transition: background 0.3s ease, color 0.3s ease;
}

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

/* ---------- NAV ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  height: var(--nav-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 22px;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav-brand {
  display: flex;
  align-items: center;
  gap: 8px;
  font-weight: 700;
  font-size: 18px;
}
.nav-logo { font-size: 20px; }
.nav-links { display: flex; gap: 22px; }
.nav-links a {
  color: var(--text-soft);
  font-weight: 500;
  transition: color 0.2s;
}
.nav-links a:hover { color: var(--accent); }
.nav-actions { display: flex; align-items: center; gap: 10px; }

.theme-toggle {
  display: inline-grid;
  place-items: center;
  width: 38px; height: 38px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg-elev);
  color: var(--text);
  cursor: pointer;
  transition: border-color 0.2s, transform 0.2s;
}
.theme-toggle:hover { border-color: var(--accent); transform: translateY(-1px); }
.theme-toggle svg { width: 18px; height: 18px; fill: none; stroke: currentColor; stroke-width: 2; stroke-linecap: round; stroke-linejoin: round; }
.icon-moon { display: none; }
[data-theme="dark"] .icon-sun { display: none; }
[data-theme="dark"] .icon-moon { display: block; }

.lang-toggle {
  min-width: 40px; height: 38px;
  padding: 0 10px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg-elev);
  color: var(--text);
  font-weight: 700;
  font-size: 13px;
  cursor: pointer;
  transition: border-color 0.2s, transform 0.2s;
}
.lang-toggle:hover { border-color: var(--accent); transform: translateY(-1px); }

.nav-burger {
  display: none;
  flex-direction: column;
  gap: 5px;
  width: 38px; height: 38px;
  padding: 9px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg-elev);
  cursor: pointer;
}
.nav-burger span { height: 2px; background: var(--text); border-radius: 2px; transition: 0.25s; }
.nav-burger[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-burger[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-burger[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ---------- HERO ---------- */
.hero {
  position: relative;
  min-height: calc(100vh - var(--nav-h));
  display: grid;
  place-items: center;
  text-align: center;
  padding: 40px 22px;
  background:
    radial-gradient(1200px 500px at 50% -10%, color-mix(in srgb, var(--accent) 18%, transparent), transparent 70%),
    radial-gradient(900px 400px at 90% 10%, color-mix(in srgb, var(--accent-2) 14%, transparent), transparent 70%);
}
.hero-inner { max-width: 640px; }
.hero-eyebrow { color: var(--text-soft); margin: 0 0 6px; font-size: 16px; }
.hero-title {
  font-size: clamp(44px, 9vw, 84px);
  line-height: 1.05;
  margin: 0;
  background: linear-gradient(120deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  letter-spacing: -1px;
}
.hero-tagline { font-size: clamp(18px, 3vw, 22px); color: var(--text); font-weight: 600; margin: 12px 0 8px; }
.hero-desc { color: var(--text-soft); margin: 0 auto 26px; max-width: 520px; }
.hero-cta { display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }

.btn {
  display: inline-block;
  padding: 12px 22px;
  border-radius: 999px;
  font-weight: 600;
  border: 1px solid transparent;
  cursor: pointer;
  transition: transform 0.18s, box-shadow 0.18s, background 0.2s;
}
.btn-primary { background: linear-gradient(120deg, var(--accent), var(--accent-2)); color: #fff; box-shadow: var(--shadow); }
.btn-primary:hover { transform: translateY(-2px); }
.btn-ghost { border-color: var(--border); color: var(--text); background: var(--bg-elev); }
.btn-ghost:hover { border-color: var(--accent); transform: translateY(-2px); }

.scroll-hint {
  position: absolute;
  bottom: 22px; left: 50%;
  transform: translateX(-50%);
  font-size: 22px;
  color: var(--text-soft);
  animation: bob 1.8s ease-in-out infinite;
}
@keyframes bob { 0%,100% { transform: translate(-50%, 0); } 50% { transform: translate(-50%, 8px); } }

/* ---------- SECTIONS ---------- */
.section { max-width: var(--maxw); margin: 0 auto; padding: 84px 22px; }
.section-title {
  font-size: clamp(26px, 5vw, 34px);
  margin: 0 0 32px;
  position: relative;
}
.section-title::after {
  content: "";
  display: block;
  width: 46px; height: 4px;
  margin-top: 10px;
  border-radius: 4px;
  background: linear-gradient(120deg, var(--accent), var(--accent-2));
}

/* ---------- ABOUT ---------- */
.about { display: grid; grid-template-columns: 1.4fr 1fr; gap: 32px; }
.about-text p { color: var(--text-soft); margin: 0 0 16px; }
.about-facts { list-style: none; margin: 0; padding: 0; display: grid; gap: 12px; }
.about-facts li {
  display: flex; justify-content: space-between; gap: 12px;
  padding: 12px 14px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 12px;
}
.about-facts strong { color: var(--text); }
.about-facts span { color: var(--text-soft); text-align: right; }

/* ---------- PROJECTS ---------- */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 20px; }
.card {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px;
  box-shadow: var(--shadow);
  transition: transform 0.2s, border-color 0.2s;
}
.card:hover { transform: translateY(-4px); border-color: var(--accent); }
.card h3 { margin: 0 0 8px; font-size: 20px; }
.card p { color: var(--text-soft); margin: 0 0 14px; font-size: 15px; }
.tags { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 14px; }
.tags span {
  font-size: 12px;
  padding: 3px 10px;
  border-radius: 999px;
  background: color-mix(in srgb, var(--accent) 14%, transparent);
  color: var(--accent);
  font-weight: 600;
}
.card-links { display: flex; gap: 16px; }
.card-links a { color: var(--accent); font-weight: 600; font-size: 14px; }
.card-links a:hover { text-decoration: underline; }

/* ---------- SKILLS ---------- */
.skills { display: flex; flex-wrap: wrap; gap: 12px; }
.chip {
  padding: 8px 16px;
  border-radius: 999px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  color: var(--text);
  font-weight: 500;
  font-size: 14px;
  transition: transform 0.18s, border-color 0.2s;
}
.chip:hover { transform: translateY(-2px); border-color: var(--accent); }

/* ---------- CONTACT ---------- */
.contact { text-align: center; }
.contact p { color: var(--text-soft); max-width: 520px; margin: 0 auto 24px; }
.socials { display: flex; justify-content: center; gap: 16px; }
.socials a {
  display: inline-grid; place-items: center;
  width: 48px; height: 48px;
  border: 1px solid var(--border);
  border-radius: 50%;
  background: var(--bg-elev);
  transition: transform 0.2s, border-color 0.2s, color 0.2s;
}
.socials a:hover { transform: translateY(-3px); border-color: var(--accent); color: var(--accent); }
.socials svg { width: 22px; height: 22px; fill: currentColor; }

/* ---------- FOOTER ---------- */
.footer {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 28px 22px 48px;
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  color: var(--text-soft);
  font-size: 14px;
  flex-wrap: wrap;
}
.to-top { color: var(--accent); font-weight: 600; }

/* ---------- REVEAL ANIMATION ---------- */
.reveal { opacity: 0; transform: translateY(20px); transition: opacity 0.6s ease, transform 0.6s ease; }
.reveal.in { opacity: 1; transform: none; }

/* ===========================================================
   AI CLASSROOM (ai.html) + homepage banner
   =========================================================== */

/* ---------- Homepage entry banner ---------- */
.learn-banner {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 20px;
  padding: 26px 28px;
  border-radius: var(--radius);
  border: 1px solid color-mix(in srgb, var(--accent) 40%, var(--border));
  background:
    radial-gradient(500px 200px at 8% 0%, color-mix(in srgb, var(--accent) 16%, transparent), transparent 70%),
    radial-gradient(500px 200px at 95% 100%, color-mix(in srgb, var(--accent-2) 14%, transparent), transparent 70%),
    var(--bg-elev);
  box-shadow: var(--shadow);
  transition: transform 0.2s, border-color 0.2s;
}
.learn-banner:hover { transform: translateY(-4px); border-color: var(--accent); }
.learn-banner-icon {
  display: grid; place-items: center;
  width: 62px; height: 62px;
  border-radius: 18px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  font-size: 34px;
  box-shadow: var(--shadow);
}
.learn-banner h3 { margin: 0 0 6px; font-size: 22px; }
.learn-banner p { margin: 0; color: var(--text-soft); font-size: 15px; }
.learn-banner-cta {
  white-space: nowrap;
  color: var(--accent);
  font-weight: 700;
  font-size: 15px;
}
@media (max-width: 560px) {
  .learn-banner { grid-template-columns: auto 1fr; }
  .learn-banner-cta { grid-column: 1 / -1; }
}

/* ---------- AI page hero tweak ---------- */
.hero-learn {
  background:
    radial-gradient(1200px 500px at 50% -10%, color-mix(in srgb, var(--accent-2) 20%, transparent), transparent 70%),
    radial-gradient(900px 400px at 10% 20%, color-mix(in srgb, var(--accent) 16%, transparent), transparent 70%);
}

/* ---------- Concept TOC ---------- */
.toc { display: flex; flex-wrap: wrap; gap: 10px; margin: 0 0 40px; }
.toc a {
  padding: 7px 14px;
  border-radius: 999px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  color: var(--text);
  font-weight: 600;
  font-size: 14px;
  transition: transform 0.18s, border-color 0.2s, color 0.2s;
}
.toc a:hover { transform: translateY(-2px); border-color: var(--accent); color: var(--accent); }

/* ---------- Concept cards ---------- */
.concept {
  display: grid;
  grid-template-columns: 1.15fr 1fr;
  gap: 28px;
  align-items: center;
  padding: 30px;
  margin-bottom: 34px;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}
.concept-title { display: flex; align-items: center; gap: 14px; margin: 0 0 18px; font-size: 24px; }
.concept-no {
  display: grid; place-items: center;
  flex: none;
  width: 42px; height: 42px;
  border-radius: 12px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #fff;
  font-size: 20px;
  font-weight: 800;
}
.analogy, .explain { margin-bottom: 16px; }
.analogy .label, .explain .label {
  margin: 0 0 4px;
  font-size: 13px;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--accent);
}
.explain .label { color: var(--accent-2); }
.analogy p, .explain p { margin: 0; color: var(--text-soft); font-size: 15.5px; }
.tip {
  margin: 0;
  padding: 12px 14px;
  border-left: 4px solid #f9ca24;
  border-radius: 8px;
  background: color-mix(in srgb, #f9ca24 10%, transparent);
  color: var(--text-soft);
  font-size: 14.5px;
}
.tip strong { color: var(--text); }

/* ---------- Figures (shared) ---------- */
.fig {
  display: grid;
  place-items: center;
  min-height: 220px;
  padding: 18px;
  border-radius: 12px;
  background: var(--bg-soft);
  border: 1px solid var(--border);
}
.fig-svg { width: 100%; max-width: 340px; height: auto; }
.fig-text { fill: var(--text); font-size: 15px; font-weight: 700; font-family: inherit; }
.fig-text.big { font-size: 19px; letter-spacing: 0.08em; }
.fig-text.small { fill: var(--text-soft); font-size: 12px; font-weight: 500; }

/* robot: blink + glow */
.eye { transform-box: fill-box; transform-origin: center; animation: blink 4.5s infinite; }
@keyframes blink { 0%, 91%, 100% { transform: scaleY(1); } 95% { transform: scaleY(0.08); } }
.pulse { animation: pulseGlow 2s ease-in-out infinite; }
@keyframes pulseGlow { 0%, 100% { opacity: 0.35; } 50% { opacity: 1; } }

/* model: books on a conveyor */
.book { animation: bookSlide 3.6s linear infinite; }
.book.b2 { animation-delay: -1.2s; }
.book.b3 { animation-delay: -2.4s; }
@keyframes bookSlide {
  0% { transform: translateX(0); opacity: 0; }
  8% { opacity: 1; }
  88% { opacity: 1; }
  100% { transform: translateX(155px); opacity: 0; }
}

/* agent: orbiting dot */
.orbit {
  transform-box: view-box;
  transform-origin: 160px 110px;
  animation: orbit 6s linear infinite;
}
@keyframes orbit { to { transform: rotate(360deg); } }

/* prompt: chat demo with typing */
.chat-demo { width: 100%; max-width: 340px; display: grid; gap: 14px; }
.chat-row { display: flex; align-items: flex-end; gap: 10px; }
.chat-row:last-child { flex-direction: row-reverse; }
.chat-face { font-size: 28px; line-height: 1; }
.bubble {
  padding: 12px 14px;
  border-radius: 14px;
  font-size: 15px;
  min-height: 22px;
  min-width: 120px;
}
.bubble-user {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #fff;
  border-bottom-left-radius: 4px;
}
.bubble-ai {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-bottom-right-radius: 4px;
  display: flex;
  align-items: center;
}
.caret {
  display: inline-block;
  width: 2px; height: 1.05em;
  margin-left: 2px;
  vertical-align: -0.15em;
  background: #fff;
  animation: caretBlink 1s steps(1) infinite;
}
@keyframes caretBlink { 50% { opacity: 0; } }
.dots { display: inline-flex; gap: 5px; }
.dots i {
  width: 7px; height: 7px;
  border-radius: 50%;
  background: var(--text-soft);
  animation: dotJump 1.2s ease-in-out infinite;
}
.dots i:nth-child(2) { animation-delay: 0.15s; }
.dots i:nth-child(3) { animation-delay: 0.3s; }
@keyframes dotJump { 0%, 60%, 100% { transform: none; } 30% { transform: translateY(-6px); } }

/* token: chips demo */
.tok-demo { text-align: center; width: 100%; }
.tok-label { margin: 0 0 6px; color: var(--text-soft); font-size: 13px; font-weight: 700; letter-spacing: 0.05em; }
.tok-sentence { margin: 0 0 10px; font-size: 20px; font-weight: 700; }
.tok-arrow { margin: 0 0 14px; color: var(--text-soft); font-size: 14px; font-weight: 600; }
.tok-row { display: flex; flex-wrap: wrap; gap: 10px; justify-content: center; }
.tok {
  padding: 8px 14px;
  border-radius: 12px;
  color: #fff;
  font-weight: 800;
  font-size: 17px;
  box-shadow: 0 4px 12px rgba(20, 23, 33, 0.18);
  animation: tokPop 2.4s ease-in-out infinite;
}
.tok.t1 { background: #ff7675; }
.tok.t2 { background: #fdcb6e; animation-delay: 0.2s; }
.tok.t3 { background: #55efc4; animation-delay: 0.4s; }
.tok.t4 { background: #74b9ff; animation-delay: 0.6s; }
@keyframes tokPop {
  0%, 22%, 100% { transform: none; }
  11% { transform: translateY(-9px) scale(1.08); }
}

/* training: checks + bar */
.train-demo { width: 100%; max-width: 300px; text-align: center; }
.train-steps { display: flex; justify-content: center; gap: 10px; font-size: 24px; margin-bottom: 16px; min-height: 34px; }
.check { opacity: 0; animation: checkPop 5s linear infinite; }
.check.ck2 { animation-delay: 0.7s; }
.check.ck3 { animation-delay: 1.4s; }
.check.ck4 { animation-delay: 2.1s; }
.check.ck5 { animation-delay: 2.8s; }
@keyframes checkPop {
  0% { opacity: 0; transform: scale(0); }
  2% { opacity: 1; transform: scale(1.35); }
  5% { transform: scale(1); }
  92% { opacity: 1; }
  100% { opacity: 0; }
}
.train-bar {
  height: 16px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg-elev);
  overflow: hidden;
}
.train-fill {
  height: 100%;
  width: 0;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  animation: trainFill 5s ease-in-out infinite;
}
@keyframes trainFill {
  0% { width: 3%; }
  75% { width: 96%; }
  100% { width: 96%; }
}
.train-label { margin: 12px 0 0; color: var(--text-soft); font-size: 14px; font-weight: 600; }

/* ---------- Quiz ---------- */
.quiz-desc { color: var(--text-soft); margin: -16px 0 28px; }
.quiz-q {
  padding: 22px;
  margin-bottom: 18px;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.quiz-question { margin: 0 0 14px; font-size: 17px; font-weight: 700; }
.quiz-opts { display: flex; flex-wrap: wrap; gap: 10px; }
.quiz-opt {
  padding: 10px 18px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg-soft);
  color: var(--text);
  font-family: inherit;
  font-size: 15px;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.15s, border-color 0.2s, background 0.2s;
}
.quiz-opt:hover:not(:disabled) { transform: translateY(-2px); border-color: var(--accent); }
.quiz-opt:disabled { cursor: default; opacity: 0.85; }
.quiz-opt.right {
  background: color-mix(in srgb, #55efc4 30%, var(--bg-elev));
  border-color: #00b894;
  color: var(--text);
  opacity: 1;
}
.quiz-opt.wrong {
  background: color-mix(in srgb, #ff7675 25%, var(--bg-elev));
  border-color: #d63031;
  opacity: 1;
}
.quiz-fb { margin: 14px 0 0; font-weight: 700; font-size: 15px; visibility: hidden; min-height: 4px; }
.quiz-fb.show { visibility: visible; }
.quiz-fb.ok { color: #00b894; }
.quiz-fb.no { color: #d63031; }
.quiz-score {
  margin: 10px 0 22px;
  font-size: 19px;
  font-weight: 800;
  background: linear-gradient(120deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  visibility: hidden;
}
.quiz-score.show { visibility: visible; }

/* ---------- AI page responsive ---------- */
@media (max-width: 760px) {
  .concept { grid-template-columns: 1fr; }
  .fig { order: -1; }
  .concept-title { font-size: 20px; }
}

/* ---------- RESPONSIVE ---------- */
@media (max-width: 720px) {
  .nav-links {
    position: fixed;
    inset: var(--nav-h) 0 auto 0;
    flex-direction: column;
    gap: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    padding: 8px 22px 16px;
    transform: translateY(-120%);
    transition: transform 0.28s ease;
  }
  .nav-links.open { transform: translateY(0); }
  .nav-links a { padding: 12px 0; border-bottom: 1px solid var(--border); }
  .nav-burger { display: flex; }
  .about { grid-template-columns: 1fr; }
}
@media (prefers-reduced-motion: reduce) {
  * { animation: none !important; scroll-behavior: auto !important; }
  .reveal { opacity: 1; transform: none; transition: none; }
}
.giscus {
  padding: 0 30px;
}