:root{
  --blue-50:#eff6ff; --blue-100:#dbeafe; --blue-500:#3b82f6;
  --blue-600:#2563eb; --blue-700:#1d4ed8; --blue-800:#1e40af;
  --ink:#0f172a; --slate:#475569; --muted:#64748b;
  --line:#e2e8f0; --bg:#f8fafc; --card:#ffffff;
  --good:#16a34a; --good-bg:#dcfce7; --bad:#dc2626; --bad-bg:#fee2e2;
  --shadow:0 1px 2px rgba(15,23,42,.04), 0 8px 24px rgba(15,23,42,.06);
  --radius:16px;
}
*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{
  font-family:system-ui,-apple-system,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  color:var(--ink); background:var(--bg); line-height:1.55;
  -webkit-font-smoothing:antialiased;
}
a{color:inherit;text-decoration:none}
.container{width:min(1120px,92vw);margin-inline:auto}
.container.narrow{width:min(760px,92vw)}
.hidden{display:none !important}

/* buttons */
.btn{display:inline-flex;align-items:center;gap:.4rem;justify-content:center;
  border:1px solid transparent;border-radius:10px;padding:.7rem 1.2rem;
  font-weight:600;font-size:.95rem;cursor:pointer;transition:.15s;white-space:nowrap}
.btn-sm{padding:.5rem .9rem;font-size:.88rem}
.btn-primary{background:var(--blue-600);color:#fff;box-shadow:0 6px 16px rgba(37,99,235,.25)}
.btn-primary:hover{background:var(--blue-700)}
.btn-ghost{background:#fff;border-color:var(--line);color:var(--ink)}
.btn-ghost:hover{border-color:var(--blue-500);color:var(--blue-700)}
.btn:disabled{opacity:.45;cursor:not-allowed}

/* header */
.site-header{position:sticky;top:0;z-index:50;background:rgba(255,255,255,.85);
  backdrop-filter:blur(10px);border-bottom:1px solid var(--line)}
.header-inner{display:flex;align-items:center;gap:1.5rem;padding:.8rem 0}
.brand{display:flex;align-items:center;gap:.55rem}
.brand-mark{width:32px;height:32px;border-radius:8px}
.brand-name{font-weight:800;font-size:1.25rem;letter-spacing:-.02em}
.brand-name span{color:var(--blue-600)}
.main-nav{display:flex;gap:1.4rem;margin-left:auto;font-weight:500;color:var(--slate)}
.main-nav a{padding:.3rem 0;border-bottom:2px solid transparent}
.main-nav a:hover{color:var(--blue-700)}
.main-nav a.active{color:var(--blue-700);border-color:var(--blue-600)}

/* hero */
.hero{background:linear-gradient(160deg,var(--blue-50),#fff 70%);
  border-bottom:1px solid var(--line);padding:4.5rem 0 3.5rem}
.hero-inner{text-align:center;max-width:780px;margin-inline:auto}
.pill{display:inline-block;background:var(--blue-100);color:var(--blue-800);
  font-weight:600;font-size:.8rem;padding:.35rem .85rem;border-radius:999px;
  letter-spacing:.02em}
.hero h1{font-size:clamp(2rem,5vw,3.2rem);line-height:1.1;margin:1.1rem 0;
  letter-spacing:-.03em;font-weight:800}
.accent{color:var(--blue-600)}
.lead{font-size:1.12rem;color:var(--slate);max-width:620px;margin:0 auto}
.hero-cta{display:flex;gap:.8rem;justify-content:center;margin-top:1.8rem;flex-wrap:wrap}
.hero-stats{display:flex;gap:2.5rem;justify-content:center;margin-top:2.6rem;flex-wrap:wrap}
.hero-stats .stat{text-align:center}
.hero-stats .stat b{display:block;font-size:1.8rem;color:var(--blue-700);font-weight:800}
.hero-stats .stat span{font-size:.85rem;color:var(--muted)}

/* sections */
.section-title{font-size:1.6rem;font-weight:800;letter-spacing:-.02em;margin-top:3rem}
.section-sub{color:var(--muted);margin:.3rem 0 1.4rem}

/* subject grid */
.subject-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(220px,1fr));gap:1rem}
.subject-card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);
  padding:1.3rem;cursor:pointer;transition:.18s;box-shadow:var(--shadow)}
.subject-card:hover{transform:translateY(-3px);border-color:var(--blue-500)}
.subject-card .ico{font-size:1.8rem}
.subject-card h3{font-size:1.05rem;margin:.6rem 0 .2rem}
.subject-card p{font-size:.85rem;color:var(--muted)}
.subject-card .count{display:inline-block;margin-top:.7rem;font-size:.78rem;font-weight:600;
  color:var(--blue-700);background:var(--blue-50);padding:.2rem .6rem;border-radius:999px}

/* year grid */
.year-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(130px,1fr));gap:.8rem}
.year-card{background:var(--card);border:1px solid var(--line);border-radius:12px;
  padding:1rem;text-align:center;cursor:pointer;transition:.18s;box-shadow:var(--shadow)}
.year-card:hover{border-color:var(--blue-500);transform:translateY(-2px)}
.year-card b{font-size:1.4rem;display:block;color:var(--ink)}
.year-card span{font-size:.78rem;color:var(--muted)}

/* why */
.why{margin:1rem 0 3rem}
.why-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:1rem;margin-top:1.4rem}
.why-card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);padding:1.4rem}
.why-ico{font-size:1.6rem}
.why-card h3{font-size:1.02rem;margin:.5rem 0 .3rem}
.why-card p{font-size:.88rem;color:var(--muted)}

/* quiz */
.quiz-shell{max-width:760px;padding:2.5rem 0 3rem}
.quiz-topbar{display:flex;justify-content:space-between;align-items:center;gap:1rem;
  margin-bottom:1.4rem;flex-wrap:wrap}
.quiz-meta{font-weight:700;color:var(--blue-700)}
.quiz-meta small{display:block;font-weight:500;color:var(--muted);font-size:.78rem}
.quiz-progress{display:flex;align-items:center;gap:.7rem;min-width:200px;flex:1;max-width:320px}
.quiz-progress-bar{flex:1;height:8px;background:var(--blue-100);border-radius:999px;overflow:hidden}
.quiz-progress-bar span{display:block;height:100%;background:var(--blue-600);width:0;transition:.3s}
.quiz-count{font-size:.82rem;color:var(--muted);font-weight:600;white-space:nowrap}

.qcard{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);
  padding:1.8rem;box-shadow:var(--shadow)}
.qtags{display:flex;gap:.5rem;flex-wrap:wrap;margin-bottom:1rem}
.qtag{font-size:.72rem;font-weight:600;background:var(--blue-50);color:var(--blue-700);
  padding:.22rem .6rem;border-radius:999px}
.qtext{font-size:1.12rem;font-weight:600;white-space:pre-line;line-height:1.5;margin-bottom:1.3rem}
.options{display:flex;flex-direction:column;gap:.65rem}
.option{display:flex;align-items:flex-start;gap:.8rem;border:1.5px solid var(--line);
  border-radius:12px;padding:.85rem 1rem;cursor:pointer;transition:.12s;background:#fff;text-align:left;font-size:.98rem}
.option:hover{border-color:var(--blue-500);background:var(--blue-50)}
.option .key{flex:none;width:26px;height:26px;border-radius:50%;border:1.5px solid var(--line);
  display:grid;place-items:center;font-weight:700;font-size:.8rem;color:var(--slate)}
.option.correct{border-color:var(--good);background:var(--good-bg)}
.option.correct .key{background:var(--good);color:#fff;border-color:var(--good)}
.option.wrong{border-color:var(--bad);background:var(--bad-bg)}
.option.wrong .key{background:var(--bad);color:#fff;border-color:var(--bad)}
.option.locked{cursor:default;pointer-events:none}
.option.dim{opacity:.6}

.explain{margin-top:1.6rem;border-top:1px dashed var(--line);padding-top:1.3rem}
.explain.hidden{display:none}
.explain .verdict{font-weight:700;margin-bottom:.9rem;font-size:1rem;line-height:1.5}
.explain .verdict.ok{color:var(--good)}
.explain .verdict.no{color:var(--bad)}
.explain p{font-size:.95rem;color:var(--slate);line-height:1.75;
  background:var(--blue-50);border:1px solid var(--blue-100);border-radius:12px;padding:1rem 1.1rem}
.explain .lbl{font-weight:700;color:var(--ink);display:block;margin-bottom:.35rem}

.quiz-nav{display:flex;gap:.7rem;margin-top:1.2rem;align-items:center;
  position:sticky;bottom:0;background:var(--bg);
  padding:.9rem 0;border-top:1px solid var(--line);z-index:20}
.quiz-nav #btn-quit{margin-left:auto}

/* results */
.result-card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);
  padding:2.5rem;text-align:center;max-width:620px;margin:3rem auto;box-shadow:var(--shadow)}
.result-card .score-ring{font-size:3.2rem;font-weight:800;color:var(--blue-700)}
.result-card h2{font-size:1.5rem;margin:.5rem 0}
.result-card .sub{color:var(--muted);margin-bottom:1.6rem}
.result-breakdown{display:flex;justify-content:center;gap:2rem;margin:1.4rem 0;flex-wrap:wrap}
.result-breakdown div b{display:block;font-size:1.5rem}
.result-breakdown .r-ok b{color:var(--good)}
.result-breakdown .r-no b{color:var(--bad)}
.result-breakdown .r-sk b{color:var(--muted)}
.result-breakdown span{font-size:.82rem;color:var(--muted)}
.result-actions{display:flex;gap:.8rem;justify-content:center;margin-top:1rem;flex-wrap:wrap}

/* about / prose */
.prose{color:var(--slate);margin:1rem 0;font-size:1rem}
.prose code{background:var(--blue-50);padding:.1rem .4rem;border-radius:6px;font-size:.9em}
.prose strong{color:var(--ink)}

/* seo block */
.seo-block{margin:1rem 0 1rem;max-width:880px}

/* faq */
.faq{margin:1rem 0 3rem;max-width:880px}
.faq-item{background:var(--card);border:1px solid var(--line);border-radius:12px;
  padding:.2rem 1.2rem;margin-bottom:.7rem;box-shadow:var(--shadow)}
.faq-item summary{list-style:none;cursor:pointer;font-weight:700;padding:1rem 0;
  display:flex;justify-content:space-between;align-items:center;gap:1rem}
.faq-item summary::-webkit-details-marker{display:none}
.faq-item summary::after{content:"+";color:var(--blue-600);font-size:1.4rem;font-weight:700;line-height:1}
.faq-item[open] summary::after{content:"–"}
.faq-item p{color:var(--slate);font-size:.95rem;padding:0 0 1.1rem;margin:0}

/* footer */
.site-footer{background:#0b1220;color:#cbd5e1;margin-top:3rem}
.footer-inner{display:flex;justify-content:space-between;gap:2rem;padding:2.5rem 0;flex-wrap:wrap}
.footer-brand .brand-name{color:#fff}
.footer-brand p{font-size:.85rem;color:#94a3b8;margin-top:.5rem}
.footer-brand{display:flex;flex-direction:column;gap:.2rem}
.footer-brand .brand-mark{width:30px;height:30px}
.footer-links{display:flex;gap:1.4rem;flex-wrap:wrap;align-items:flex-start}
.footer-links a{color:#cbd5e1;font-size:.9rem}
.footer-links a:hover{color:#fff}
.footer-bottom{border-top:1px solid #1e293b;text-align:center;padding:1rem;font-size:.8rem;color:#64748b}

/* ============================================================
   GAMIFICATION
   ============================================================ */
/* header game stats */
.game-stats{display:flex;align-items:center;gap:.5rem;margin-left:auto}
.main-nav + .game-stats{margin-left:1.2rem}
.gs-item{display:flex;align-items:center;gap:.25rem;font-weight:800;font-size:.95rem;
  background:var(--blue-50);border:1px solid var(--line);border-radius:999px;padding:.3rem .7rem}
.gs-item b{font-weight:800}
.gs-streak{color:#ea580c;background:#fff7ed;border-color:#fed7aa}
.gs-xp{color:var(--blue-700)}
.gs-hearts{color:#dc2626;background:#fef2f2;border-color:#fecaca}
.gs-mute{border:1px solid var(--line);background:#fff;border-radius:999px;cursor:pointer;
  width:34px;height:34px;font-size:1rem;line-height:1}
.gs-mute:hover{border-color:var(--blue-500)}

/* home game panel */
.game-panel{display:grid;grid-template-columns:repeat(auto-fit,minmax(190px,1fr));gap:1rem;
  margin:0 0 .5rem}
.gp-card{display:flex;align-items:center;gap:.9rem;background:var(--card);border:1px solid var(--line);
  border-radius:var(--radius);padding:1.1rem 1.2rem;box-shadow:var(--shadow)}
.gp-ico{font-size:1.9rem;flex:none}
.gp-meta{display:flex;flex-direction:column;min-width:0;flex:1}
.gp-meta b{font-size:1.35rem;font-weight:800;line-height:1.1}
.gp-meta span{font-size:.8rem;color:var(--muted)}
.gp-bar{height:7px;background:var(--blue-100);border-radius:999px;margin-top:.45rem;overflow:hidden}
.gp-bar i{display:block;height:100%;background:linear-gradient(90deg,var(--blue-500),var(--blue-700));border-radius:999px;transition:width .5s}
.gp-ring{--p:0deg;width:54px;height:54px;border-radius:50%;flex:none;display:grid;place-items:center;
  background:conic-gradient(var(--blue-600) var(--p), var(--blue-100) 0)}
.gp-ring span{width:40px;height:40px;border-radius:50%;background:#fff;display:grid;place-items:center;
  font-size:.78rem;font-weight:800;color:var(--blue-700)}

/* subtle answer feedback */
.option.correct{animation:pop .35s}
.explain.pop{animation:slideUp .35s}
@keyframes pop{0%{transform:scale(.92)}60%{transform:scale(1.04)}100%{transform:scale(1)}}
@keyframes slideUp{from{opacity:0;transform:translateY(10px)}to{opacity:1;transform:translateY(0)}}

/* floating XP + confetti + toast */
#confetti{position:fixed;inset:0;width:100%;height:100%;pointer-events:none;z-index:9998}
#fx-layer{position:fixed;inset:0;pointer-events:none;z-index:9999}
.xp-pop{position:absolute;font-weight:800;color:#16a34a;font-size:1.05rem;
  text-shadow:0 1px 2px rgba(0,0,0,.1);animation:floatUp 1.1s ease-out forwards}
@keyframes floatUp{0%{opacity:0;transform:translateY(0) scale(.8)}15%{opacity:1}100%{opacity:0;transform:translateY(-60px) scale(1.1)}}
.toast{position:fixed;left:50%;bottom:28px;transform:translateX(-50%) translateY(40px);
  background:var(--ink);color:#fff;font-weight:700;padding:.7rem 1.2rem;border-radius:999px;
  box-shadow:0 10px 30px rgba(0,0,0,.25);opacity:0;transition:.3s;z-index:10000;font-size:.92rem}
.toast.show{opacity:1;transform:translateX(-50%) translateY(0)}

/* lesson complete */
.result-emoji{font-size:3.4rem;animation:pop .5s}
.result-rewards{display:grid;grid-template-columns:repeat(3,1fr);gap:.7rem;margin:1.4rem 0}
.result-rewards .rw{background:var(--blue-50);border:1px solid var(--blue-100);border-radius:12px;padding:.8rem .4rem}
.result-rewards .rw b{display:block;font-size:1.25rem;font-weight:800;color:var(--blue-700)}
.result-rewards .rw span{font-size:.72rem;color:var(--muted)}
.result-rewards .rw-xp b{color:#16a34a}
.result-rewards .rw-streak b{color:#ea580c}

/* ============================================================
   QUESTION-BANK BROWSER (filters + list)
   ============================================================ */
.browse{display:grid;grid-template-columns:250px 1fr;gap:1.5rem;align-items:start;padding:1.6rem 0 3rem}
.filters{position:sticky;top:80px;background:var(--card);border:1px solid var(--line);
  border-radius:var(--radius);padding:1rem .8rem;box-shadow:var(--shadow);
  max-height:calc(100vh - 100px);overflow:auto}
.f-group{margin-bottom:1.1rem}
.f-group h4{font-size:.7rem;text-transform:uppercase;letter-spacing:.06em;color:var(--muted);
  margin:0 .4rem .45rem}
.f-item{display:flex;justify-content:space-between;align-items:center;gap:.5rem;width:100%;
  text-align:left;border:none;background:transparent;padding:.5rem .6rem;border-radius:9px;
  cursor:pointer;font-size:.9rem;color:var(--ink);line-height:1.3}
.f-item em{font-style:normal;font-size:.76rem;color:var(--muted);font-weight:700;flex:none}
.f-item:hover{background:var(--blue-50)}
.f-item.active{background:var(--blue-600);color:#fff;font-weight:600}
.f-item.active em{color:#dbeafe}

.qlist-head{display:flex;align-items:center;gap:.8rem;margin-bottom:1.1rem;flex-wrap:wrap}
.qlist-head h2{font-size:1.35rem;font-weight:800;letter-spacing:-.02em}
.qlist-count{color:var(--muted);font-size:.9rem;font-weight:600}
.filter-toggle{display:none}

.qlist{display:flex;flex-direction:column;gap:1.1rem}
.qlist .qcard{padding:1.5rem}
.qnum{font-weight:800;color:var(--blue-700);font-size:.74rem;background:var(--blue-50);
  padding:.2rem .55rem;border-radius:6px}
.qlist-more{text-align:center;margin:1.6rem 0 .5rem}

@media(max-width:820px){
  .browse{grid-template-columns:1fr;padding-top:1rem}
  .filters{position:fixed;left:0;top:0;bottom:0;width:82%;max-width:300px;z-index:70;
    transform:translateX(-100%);transition:transform .25s;border-radius:0;max-height:none;
    box-shadow:0 0 40px rgba(0,0,0,.25)}
  .filters.open{transform:none}
  .filter-toggle{display:inline-flex}
}

@media(max-width:640px){
  .main-nav{display:none}
  .hero{padding:3rem 0 2.5rem}
  .qcard{padding:1.3rem}
  .game-stats{margin-left:auto;gap:.35rem}
  .gs-item{padding:.28rem .55rem;font-size:.85rem}
}