:root{
  --bg:#0f1420; --bg2:#161d2e; --card:#1c2438; --line:#2a3450;
  --tx:#e8edf7; --tx2:#9aa7c0; --acc:#4f8cff; --acc2:#7c5cff;
  --ok:#2ecc71; --err:#e74c3c; --warn:#f39c12; --gold:#ffd166;
}
*{box-sizing:border-box;margin:0;padding:0}
body{font-family:'Segoe UI',system-ui,-apple-system,sans-serif;background:var(--bg);color:var(--tx);min-height:100vh}
header{position:sticky;top:0;z-index:10;background:rgba(15,20,32,.92);backdrop-filter:blur(8px);border-bottom:1px solid var(--line);padding:10px 18px;display:flex;flex-wrap:wrap;gap:10px;align-items:center;justify-content:space-between}
.logo{font-size:1.25rem;font-weight:800;display:flex;align-items:center;gap:8px}
.logo span{background:linear-gradient(90deg,var(--acc),var(--acc2));-webkit-background-clip:text;background-clip:text;color:transparent}
.logo small{font-weight:400;color:var(--tx2);font-size:.72rem}
nav{display:flex;gap:6px;flex-wrap:wrap}
nav button{background:none;border:1px solid transparent;color:var(--tx2);padding:8px 14px;border-radius:10px;cursor:pointer;font-size:.92rem;transition:.2s}
nav button:hover{color:var(--tx);background:var(--card)}
nav button.active{color:var(--tx);background:var(--card);border-color:var(--line);font-weight:600}
main{max-width:1000px;margin:0 auto;padding:24px 18px 60px}
footer{text-align:center;color:var(--tx2);font-size:.78rem;padding:20px;border-top:1px solid var(--line)}

/* cards & grids */
.grid{display:grid;gap:16px}
.grid.mods{grid-template-columns:repeat(auto-fill,minmax(280px,1fr))}
.card{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:20px;transition:.2s}
.card:hover{border-color:var(--acc);transform:translateY(-2px)}
.card .emoji{font-size:2rem}
.card h3{margin:8px 0 6px}
.card p{color:var(--tx2);font-size:.88rem;line-height:1.5}
.chips{display:flex;gap:6px;flex-wrap:wrap;margin-top:10px}
.chip{font-size:.72rem;background:var(--bg2);border:1px solid var(--line);color:var(--tx2);padding:3px 10px;border-radius:99px}
h1.page{font-size:1.5rem;margin-bottom:6px}
p.sub{color:var(--tx2);margin-bottom:22px}

/* study */
.modnav{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:20px}
.modnav button{background:var(--bg2);border:1px solid var(--line);color:var(--tx2);padding:7px 14px;border-radius:10px;cursor:pointer}
.modnav button.active{background:var(--acc);border-color:var(--acc);color:#fff;font-weight:600}
.section-list .card{margin-bottom:14px;cursor:pointer}
.secbody{margin-top:14px;color:var(--tx);line-height:1.7;font-size:.95rem}
.secbody h2{font-size:1.2rem;margin:18px 0 8px;color:var(--acc)}
.secbody h3{font-size:1.05rem;margin:14px 0 6px}
.secbody ul{margin:8px 0 8px 20px}
.secbody table{border-collapse:collapse;margin:12px 0;width:100%}
.secbody th,.secbody td{border:1px solid var(--line);padding:6px 10px;font-size:.85rem;text-align:left}
.secbody th{background:var(--bg2)}
.secbody code{background:var(--bg2);padding:1px 6px;border-radius:6px;font-size:.85em}
.keypoints{background:linear-gradient(135deg,rgba(79,140,255,.08),rgba(124,92,255,.08));border:1px solid var(--acc);border-radius:12px;padding:14px 16px;margin-top:16px}
.keypoints li{margin:6px 0 6px 18px}
.keypoints b{color:var(--gold)}

/* quiz */
.qbox{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:22px;margin-bottom:18px}
.qbox .qmeta{display:flex;gap:8px;align-items:center;margin-bottom:10px;font-size:.75rem;color:var(--tx2)}
.qbox .qmeta .diff-facil{color:var(--ok)} .qbox .qmeta .diff-media{color:var(--warn)} .qbox .qmeta .diff-dificil{color:var(--err)}
.qbox h3{font-size:1.02rem;line-height:1.5;margin-bottom:14px;font-weight:600}
.alt{display:block;width:100%;text-align:left;background:var(--bg2);border:2px solid var(--line);color:var(--tx);padding:12px 14px;border-radius:12px;margin-bottom:8px;cursor:pointer;font-size:.92rem;line-height:1.4;transition:.15s}
.alt:hover:not(:disabled){border-color:var(--acc)}
.alt:disabled{cursor:default;opacity:.9}
.alt.correct{border-color:var(--ok);background:rgba(46,204,113,.12)}
.alt.wrong{border-color:var(--err);background:rgba(231,76,60,.12)}
.expl{display:none;margin-top:12px;background:var(--bg2);border-left:4px solid var(--acc);border-radius:0 10px 10px 0;padding:12px 14px;font-size:.88rem;line-height:1.6;color:var(--tx2)}
.expl.show{display:block}
.quizbar{display:flex;justify-content:space-between;align-items:center;margin-bottom:18px;flex-wrap:wrap;gap:10px}
.pill{background:var(--bg2);border:1px solid var(--line);padding:6px 14px;border-radius:99px;font-size:.82rem;color:var(--tx2)}
.btn{background:linear-gradient(90deg,var(--acc),var(--acc2));border:none;color:#fff;font-weight:600;padding:12px 22px;border-radius:12px;cursor:pointer;font-size:.95rem;transition:.2s}
.btn:hover{filter:brightness(1.15)}
.btn.ghost{background:var(--bg2);border:1px solid var(--line);color:var(--tx)}
.result-hero{text-align:center;padding:34px;background:var(--card);border:1px solid var(--line);border-radius:16px;margin-bottom:20px}
.result-hero .big{font-size:3rem;font-weight:800}
.result-hero .pct-ok{color:var(--ok)} .result-hero .pct-mid{color:var(--warn)} .result-hero .pct-bad{color:var(--err)}

/* flashcards */
.fc-stage{perspective:1200px;max-width:640px;margin:0 auto}
.fc{position:relative;width:100%;min-height:280px;transform-style:preserve-3d;transition:transform .5s;cursor:pointer}
.fc.flipped{transform:rotateY(180deg)}
.fc-face{position:absolute;inset:0;backface-visibility:hidden;background:var(--card);border:1px solid var(--line);border-radius:18px;display:flex;align-items:center;justify-content:center;padding:30px;text-align:center;font-size:1.15rem;line-height:1.6}
.fc-back{transform:rotateY(180deg);background:linear-gradient(135deg,#1c2438,#233150);border-color:var(--acc)}
.fc-controls{display:flex;gap:10px;justify-content:center;margin-top:22px;flex-wrap:wrap}
.fc-tag{text-align:center;color:var(--tx2);font-size:.8rem;margin-bottom:12px}

/* stats */
.statgrid{display:grid;grid-template-columns:repeat(auto-fill,minmax(200px,1fr));gap:14px;margin-bottom:24px}
.stat{background:var(--card);border:1px solid var(--line);border-radius:14px;padding:18px;text-align:center}
.stat .n{font-size:2rem;font-weight:800;color:var(--acc)}
.stat .l{color:var(--tx2);font-size:.8rem;margin-top:4px}
table.stats{width:100%;border-collapse:collapse;font-size:.88rem}
table.stats th,table.stats td{border:1px solid var(--line);padding:10px 12px;text-align:left}
table.stats th{background:var(--bg2);color:var(--tx2);font-weight:600}
.bar{height:8px;background:var(--bg2);border-radius:99px;overflow:hidden;min-width:120px}
.bar>i{display:block;height:100%;background:linear-gradient(90deg,var(--acc),var(--acc2))}
.home-hero{background:linear-gradient(135deg,rgba(79,140,255,.15),rgba(124,92,255,.15));border:1px solid var(--line);border-radius:20px;padding:34px;margin-bottom:26px}
.home-hero h1{font-size:1.8rem;margin-bottom:10px}
.home-hero p{color:var(--tx2);line-height:1.6;max-width:640px}
.examgrid{grid-template-columns:repeat(auto-fill,minmax(300px,1fr))}
.exam-card{cursor:pointer}
.exam-card .nq{font-size:.8rem;color:var(--tx2)}
.best{color:var(--gold);font-size:.8rem}
@media(max-width:640px){nav button{padding:7px 10px;font-size:.8rem} main{padding:16px 12px 60px}}