:root {
  --bg: #0f1117;
  --surface: #1a1d27;
  --card: #222535;
  --border: #2e3250;
  --accent: #4f6ef7;
  --accent-hover: #6b84ff;
  --success: #22c55e;
  --error: #ef4444;
  --warning: #f59e0b;
  --text: #e2e8f0;
  --muted: #6b7280;
  --radius: 12px;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { background: var(--bg); color: var(--text); font-family: 'Segoe UI', system-ui, sans-serif; min-height: 100vh; }

/* ── AUTH ── */
#auth-screen { display: flex; align-items: center; justify-content: center; min-height: 100vh; padding: 20px; }
.auth-box { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 40px; width: 100%; max-width: 400px; }
.auth-box h1 { font-size: 1.6rem; margin-bottom: 6px; color: var(--accent); }
.auth-box p { color: var(--muted); margin-bottom: 24px; font-size: .9rem; }
.tab-row { display: flex; gap: 8px; margin-bottom: 24px; }
.tab-btn { flex: 1; padding: 9px; border: 1px solid var(--border); border-radius: 8px; background: var(--card); color: var(--muted); cursor: pointer; font-size: .9rem; transition: all .2s; }
.tab-btn.active { background: var(--accent); color: #fff; border-color: var(--accent); }
.form-group { margin-bottom: 16px; }
.form-group label { display: block; font-size: .85rem; color: var(--muted); margin-bottom: 6px; }
.form-group input { width: 100%; padding: 10px 14px; background: var(--card); border: 1px solid var(--border); border-radius: 8px; color: var(--text); font-size: .95rem; outline: none; transition: border-color .2s; }
.form-group input:focus { border-color: var(--accent); }
.btn { width: 100%; padding: 11px; background: var(--accent); color: #fff; border: none; border-radius: 8px; font-size: 1rem; cursor: pointer; transition: background .2s; }
.btn:hover { background: var(--accent-hover); }
.btn:disabled { opacity: .5; cursor: not-allowed; }
.msg { margin-top: 12px; font-size: .88rem; text-align: center; min-height: 20px; }
.msg.err { color: var(--error); }
.msg.ok { color: var(--success); }

/* ── APP SHELL ── */
#app-screen { display: none; min-height: 100vh; }
.topbar { background: var(--surface); border-bottom: 1px solid var(--border); padding: 0 24px; display: flex; align-items: center; justify-content: space-between; height: 60px; position: sticky; top: 0; z-index: 100; }
.topbar .logo { font-weight: 700; color: var(--accent); font-size: 1.1rem; }
.topbar .user-info { display: flex; align-items: center; gap: 12px; font-size: .9rem; color: var(--muted); }
.topbar .logout-btn { background: none; border: 1px solid var(--border); color: var(--muted); padding: 5px 12px; border-radius: 6px; cursor: pointer; font-size: .82rem; transition: all .2s; }
.topbar .logout-btn:hover { border-color: var(--error); color: var(--error); }
.nav-tabs { display: flex; border-bottom: 1px solid var(--border); background: var(--surface); padding: 0 24px; }
.nav-tab { padding: 14px 20px; cursor: pointer; color: var(--muted); font-size: .9rem; border-bottom: 2px solid transparent; transition: all .2s; }
.nav-tab.active { color: var(--accent); border-bottom-color: var(--accent); }
.page { display: none; padding: 24px; max-width: 860px; margin: 0 auto; }
.page.active { display: block; }

/* ── HOME / START ── */
.home-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 16px; margin-top: 8px; }
.home-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 24px; cursor: pointer; transition: all .2s; }
.home-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.home-card .icon { font-size: 2rem; margin-bottom: 12px; }
.home-card h3 { font-size: 1rem; margin-bottom: 6px; }
.home-card p { font-size: .82rem; color: var(--muted); }

/* ── QUIZ ── */
.quiz-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: 20px; flex-wrap: wrap; gap: 10px; }
.quiz-progress { font-size: .88rem; color: var(--muted); }
.progress-bar { height: 6px; background: var(--border); border-radius: 3px; margin-bottom: 24px; }
.progress-fill { height: 100%; background: var(--accent); border-radius: 3px; transition: width .4s; }
.question-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 28px; }
.question-card .q-meta { font-size: .78rem; color: var(--muted); text-transform: uppercase; letter-spacing: .05em; margin-bottom: 10px; }
.question-card .q-text { font-size: 1.05rem; line-height: 1.6; margin-bottom: 24px; }
.options-grid { display: flex; flex-direction: column; gap: 10px; }
.option-btn { background: var(--surface); border: 1px solid var(--border); border-radius: 8px; padding: 12px 16px; color: var(--text); cursor: pointer; text-align: left; font-size: .92rem; transition: all .2s; display: flex; gap: 10px; align-items: flex-start; }
.option-btn:hover:not(:disabled) { border-color: var(--accent); background: rgba(79,110,247,.08); }
.option-btn .opt-letter { background: var(--border); border-radius: 4px; padding: 1px 7px; font-size: .78rem; font-weight: 600; min-width: 24px; text-align: center; flex-shrink: 0; margin-top: 1px; }
.option-btn.correct { border-color: var(--success); background: rgba(34,197,94,.1); }
.option-btn.wrong { border-color: var(--error); background: rgba(239,68,68,.1); }
.option-btn:disabled { cursor: not-allowed; }

/* Computation input */
.comp-input-row { display: flex; align-items: center; gap: 8px; margin-bottom: 12px; }
.comp-prefix { color: var(--muted); font-size: .95rem; font-family: monospace; }
.comp-input { background: var(--card); border: 1px solid var(--border); border-radius: 8px; padding: 10px 14px; color: var(--text); font-size: 1rem; font-family: monospace; outline: none; min-width: 200px; transition: border-color .2s; }
.comp-input:focus { border-color: var(--accent); }
.comp-input.correct { border-color: var(--success); }
.comp-input.wrong { border-color: var(--error); }
.hint-box { font-size: .82rem; color: var(--muted); background: var(--surface); border-radius: 6px; padding: 8px 12px; margin-bottom: 12px; border-left: 3px solid var(--accent); }
.submit-btn { padding: 10px 28px; background: var(--accent); color: #fff; border: none; border-radius: 8px; cursor: pointer; font-size: .95rem; transition: background .2s; }
.submit-btn:hover:not(:disabled) { background: var(--accent-hover); }
.submit-btn:disabled { opacity: .5; cursor: not-allowed; }
.feedback-row { margin-top: 12px; font-size: .9rem; min-height: 20px; }
.feedback-row.ok { color: var(--success); }
.feedback-row.err { color: var(--error); }
.next-btn { margin-top: 20px; padding: 11px 32px; background: var(--accent); color: #fff; border: none; border-radius: 8px; cursor: pointer; font-size: .95rem; transition: background .2s; display: none; }
.next-btn.visible { display: inline-block; }
.next-btn:hover { background: var(--accent-hover); }

/* ── RESULTS ── */
.result-card { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 32px; text-align: center; margin-bottom: 24px; }
.result-score { font-size: 3.5rem; font-weight: 700; color: var(--accent); }
.result-label { color: var(--muted); margin-top: 6px; }
.result-note { margin-top: 16px; font-size: 1rem; }
.result-actions { display: flex; gap: 12px; justify-content: center; flex-wrap: wrap; margin-top: 20px; }
.result-actions button { padding: 10px 24px; border-radius: 8px; cursor: pointer; font-size: .92rem; transition: all .2s; }
.btn-outline { background: none; border: 1px solid var(--accent); color: var(--accent); }
.btn-outline:hover { background: var(--accent); color: #fff; }

/* ── STATISTIK ── */
.stats-summary { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 12px; margin-bottom: 24px; }
.stat-box { background: var(--card); border: 1px solid var(--border); border-radius: var(--radius); padding: 20px; text-align: center; }
.stat-box .val { font-size: 2rem; font-weight: 700; color: var(--accent); }
.stat-box .lbl { font-size: .8rem; color: var(--muted); margin-top: 4px; }
table { width: 100%; border-collapse: collapse; background: var(--card); border-radius: var(--radius); overflow: hidden; border: 1px solid var(--border); }
table th { background: var(--surface); padding: 12px 16px; text-align: left; font-size: .82rem; color: var(--muted); text-transform: uppercase; letter-spacing: .04em; }
table td { padding: 12px 16px; border-top: 1px solid var(--border); font-size: .9rem; }
.pct-good { color: var(--success); font-weight: 600; }
.pct-mid { color: var(--warning); font-weight: 600; }
.pct-bad { color: var(--error); font-weight: 600; }

/* ── ASCII TABLE ── */
.ascii-section { margin-top: 20px; }
.ascii-section summary { cursor: pointer; color: var(--accent); font-size: .88rem; padding: 6px 0; }
.ascii-table-wrap { overflow-x: auto; margin-top: 8px; }
.ascii-table-wrap table { font-size: .75rem; }
.ascii-table-wrap table th { font-size: .72rem; padding: 6px 8px; }
.ascii-table-wrap table td { padding: 4px 8px; font-family: monospace; }

/* ── DAMEN ── */
.chess-grid { display: inline-grid; border: 2px solid var(--border); border-radius: 4px; overflow: hidden; }
.chess-cell { width: 44px; height: 44px; display: flex; align-items: center; justify-content: center; font-size: 1.3rem; cursor: pointer; transition: background .15s; user-select: none; }
.chess-cell.light { background: #c8d8e8; }
.chess-cell.dark { background: #4a6080; }
.chess-cell.locked { cursor: not-allowed; }
.chess-cell.conflict { background: rgba(239,68,68,.45) !important; }
.chess-cell.queen-ok .chess-cell.conflict { }
.queens-task { margin-bottom: 28px; }
.queens-task .q-meta { font-size: .78rem; color: var(--muted); text-transform: uppercase; margin-bottom: 6px; }
.queens-info { font-size: .85rem; color: var(--muted); margin: 10px 0; }
.queens-btn-row { display: flex; gap: 10px; margin-top: 12px; flex-wrap: wrap; }

/* responsive */
@media (max-width: 600px) {
  .page { padding: 16px; }
  .question-card { padding: 18px; }
  .chess-cell { width: 36px; height: 36px; font-size: 1rem; }
}