:root { --bg:#f4f6fb; --card:#fff; --text:#1c2333; --muted:#6b7280;
        --primary:#3b5bdb; --primary-h:#364fc7; --ok:#2f9e44; --bad:#e03131; --border:#e2e8f0; }
* { box-sizing:border-box; }
body { margin:0; font-family:system-ui,"Segoe UI",Roboto,sans-serif;
       background:var(--bg); color:var(--text); min-height:100vh; display:flex; flex-direction:column; }
nav { background:var(--card); border-bottom:1px solid var(--border);
      display:flex; gap:1rem; align-items:center; padding:.6rem 1.2rem; }
nav .brand { font-weight:700; font-size:1.1rem; color:var(--primary); text-decoration:none; }
nav a { color:var(--text); text-decoration:none; opacity:.8; } nav a:hover { opacity:1; }
main { flex:1; width:min(760px,92vw); margin:1.5rem auto; }
footer { text-align:center; color:var(--muted); padding:1rem; font-size:.85rem; }
h1 { margin-top:0; } a { color:var(--primary); }
.muted { color:var(--muted); } .center { text-align:center; }
.crumbs { color:var(--muted); font-size:.9rem; }
.error { background:#ffe3e3; color:var(--bad); padding:.6rem 1rem; border-radius:8px; }
.card { background:var(--card); border:1px solid var(--border); border-radius:12px;
        padding:1.5rem; margin:1rem 0; box-shadow:0 1px 3px rgb(16 24 40 / 6%); }
label { display:block; margin:.8rem 0; }
label input, textarea { width:100%; padding:.55rem .7rem; margin-top:.25rem;
        border:1px solid var(--border); border-radius:8px; font:inherit; }
button, .btn { background:var(--primary); border:none; color:#fff; cursor:pointer;
        padding:.55rem 1.1rem; border-radius:8px; font:inherit; text-decoration:none;
        display:inline-block; margin-top:.4rem; }
button:hover, .btn:hover { background:var(--primary-h); }
button.success { background:var(--ok); } button.danger { background:var(--bad); }
table { width:100%; border-collapse:collapse; background:var(--card);
        border:1px solid var(--border); border-radius:12px; overflow:hidden; }
th,td { padding:.6rem .8rem; text-align:left; border-bottom:1px solid var(--border); }
th { background:#f8fafc; font-size:.85rem; text-transform:uppercase;
     letter-spacing:.04em; color:var(--muted); }
.flashcard { perspective:1000px; cursor:pointer; max-width:480px; margin:1.5rem auto; }
.flashcard .inner { position:relative; height:240px; transform-style:preserve-3d; transition:transform .5s; }
.flashcard.flipped .inner { transform:rotateY(180deg); }
.flashcard .face { position:absolute; inset:0; backface-visibility:hidden; display:flex;
        flex-direction:column; align-items:center; justify-content:center;
        background:var(--card); border:1px solid var(--border); border-radius:16px;
        box-shadow:0 4px 12px rgb(16 24 40 / 8%); }
.flashcard .back { transform:rotateY(180deg); background:#eef2ff; }
.study-actions { display:flex; gap:1rem; justify-content:center; }
.study-actions form { display:inline; }
.options { display:grid; grid-template-columns:1fr 1fr; gap:.8rem; }
.options button { width:100%; margin:0; padding:.9rem; font-size:1.05rem; }
@media (max-width:500px) { .options { grid-template-columns:1fr; } }
.feedback { border-radius:10px; padding:.7rem 1rem; margin:1rem 0; }
.feedback.ok { background:#d3f9d8; color:#1b5e20; }
.feedback.bad { background:#ffe3e3; color:var(--bad); }