:root{
    --navy:#0F2A44;
    --navy-deep:#0A1D30;
    --line:#5B8FB0;
    --line-bright:#8FC1E0;
    --paper:#F3EEE1;
    --paper-dark:#E4DCC8;
    --ink:#1B1B16;
    --ink-soft:#4A4A3E;
    --brass:#C9A24B;
    --brass-dark:#9C7A34;
    --stamp-red:#A83E3E;
    --stamp-green:#3B6E4F;
    --radius:3px;
  }
  *{box-sizing:border-box;}
  html{-webkit-text-size-adjust:100%;}
  html,body{margin:0;padding:0;overflow-x:hidden;}
  body{-webkit-tap-highlight-color:transparent;}
  body{
    background-color:var(--navy);
    background-image:
      repeating-linear-gradient(0deg, rgba(95,150,180,0.10) 0px, rgba(95,150,180,0.10) 1px, transparent 1px, transparent 32px),
      repeating-linear-gradient(90deg, rgba(95,150,180,0.10) 0px, rgba(95,150,180,0.10) 1px, transparent 1px, transparent 32px),
      radial-gradient(ellipse at top, var(--navy) 0%, var(--navy-deep) 100%);
    color:var(--paper);
    font-family:'Inter',sans-serif;
    min-height:100vh;
    padding:24px 16px 60px;
  }
  .sheet{max-width:920px;margin:0 auto;}
  .titleblock{
    border:2px solid var(--line-bright);
    border-radius:var(--radius);
    padding:18px 22px;
    margin-bottom:22px;
    display:flex;
    flex-wrap:wrap;
    justify-content:space-between;
    align-items:flex-end;
    gap:12px;
    background:rgba(255,255,255,0.02);
  }
  .titleblock h1{
    font-family:'Zilla Slab',serif;
    font-weight:700;
    font-size:1.7rem;
    margin:0 0 4px;
    letter-spacing:0.02em;
    color:var(--paper);
  }
  .titleblock .sub{
    font-size:0.85rem;
    color:var(--line-bright);
    font-family:'IBM Plex Mono',monospace;
    letter-spacing:0.03em;
  }
  .tb-meta{
    font-family:'IBM Plex Mono',monospace;
    font-size:0.72rem;
    text-align:right;
    color:var(--line-bright);
    line-height:1.6;
  }
  .tb-meta span{color:var(--brass);}
  nav.tabs{
    display:flex;
    gap:6px;
    flex-wrap:wrap;
    margin-bottom:18px;
  }
  nav.tabs button{
    font-family:'IBM Plex Mono',monospace;
    font-size:0.75rem;
    letter-spacing:0.04em;
    text-transform:uppercase;
    background:rgba(255,255,255,0.04);
    border:1px solid var(--line);
    color:var(--line-bright);
    padding:9px 14px;
    border-radius:var(--radius) var(--radius) 0 0;
    cursor:pointer;
    transition:all .15s ease;
    touch-action:manipulation;
    white-space:nowrap;
  }
  nav.tabs button:hover{background:rgba(143,193,224,0.15);}
  nav.tabs button.active{
    background:var(--paper);
    color:var(--ink);
    border-color:var(--paper);
    font-weight:600;
  }
  main{
    background:var(--paper);
    color:var(--ink);
    border-radius:0 var(--radius) var(--radius) var(--radius);
    padding:26px;
    min-height:420px;
    box-shadow:0 12px 40px rgba(0,0,0,0.35);
  }
  h2.section-title{
    font-family:'Zilla Slab',serif;
    font-size:1.3rem;
    margin:0 0 4px;
    border-bottom:2px solid var(--ink);
    padding-bottom:8px;
  }
  .note{font-size:0.85rem;color:var(--ink-soft);margin:8px 0 18px;line-height:1.5;overflow-wrap:break-word;}
  /* Flashcards */
  .flash-wrap{display:flex;flex-direction:column;align-items:center;gap:16px;}
  .flash-progress{font-family:'IBM Plex Mono',monospace;font-size:0.8rem;color:var(--ink-soft);}
  .card-scene{width:100%;max-width:480px;height:260px;-webkit-perspective:1200px;perspective:1200px;}
  .flashcard{
    width:100%;height:100%;position:relative;
    transform-style:preserve-3d;
    transition:transform .5s cubic-bezier(.4,.2,.2,1);
    cursor:pointer;
  }
  .flashcard.flipped{transform:rotateY(180deg);}
  .face{
    position:absolute;inset:0;
    -webkit-backface-visibility:hidden;
    backface-visibility:hidden;
    border:2px solid var(--ink);
    border-radius:6px;
    background:var(--paper-dark);
    display:flex;align-items:center;justify-content:center;
    text-align:center;padding:24px;
    box-shadow:4px 4px 0 rgba(0,0,0,0.15);
    overflow-y:auto;
  }
  .face .txt{overflow-wrap:break-word;word-break:break-word;}
  .face .tag{position:absolute;top:10px;left:14px;font-family:'IBM Plex Mono',monospace;font-size:0.65rem;color:var(--brass-dark);text-transform:uppercase;letter-spacing:0.05em;}
  .face .txt{font-family:'Zilla Slab',serif;font-size:1.25rem;font-weight:600;}
  .face.back{transform:rotateY(180deg);}
  .face.back .txt{font-family:'Inter',sans-serif;font-size:0.98rem;font-weight:400;line-height:1.5;}
  .flash-controls{display:flex;gap:10px;flex-wrap:wrap;justify-content:center;}
  button.btn{
    font-family:'Inter',sans-serif;
    font-weight:600;
    font-size:0.85rem;
    border:2px solid var(--ink);
    background:var(--paper);
    color:var(--ink);
    padding:9px 16px;
    border-radius:var(--radius);
    cursor:pointer;
    transition:all .12s ease;
    touch-action:manipulation;
    min-height:44px;
  }
  button.btn:hover{background:var(--ink);color:var(--paper);}
  button.btn.brass{background:var(--brass);border-color:var(--brass-dark);}
  button.btn.brass:hover{background:var(--brass-dark);}
  button.btn.stamp-green{background:var(--stamp-green);color:var(--paper);border-color:var(--stamp-green);}
  button.btn.stamp-red{background:var(--stamp-red);color:var(--paper);border-color:var(--stamp-red);}
  button.btn:disabled{opacity:0.4;cursor:not-allowed;}
  /* Math */
  .prob-card{border:2px solid var(--ink);border-radius:6px;padding:20px;background:var(--paper-dark);margin-bottom:14px;}
  .prob-card .cat{font-family:'IBM Plex Mono',monospace;font-size:0.7rem;text-transform:uppercase;color:var(--brass-dark);letter-spacing:0.05em;}
  .prob-card h3{font-family:'Zilla Slab',serif;margin:6px 0 10px;}
  .prob-card p{line-height:1.55;}
  .steps{margin-top:14px;padding-top:14px;border-top:1px dashed var(--ink-soft);font-family:'IBM Plex Mono',monospace;font-size:0.85rem;line-height:1.8;display:none;}
  .steps.show{display:block;}
  .answer-line{font-weight:700;margin-top:8px;color:var(--stamp-green);}
  .nav-row{display:flex;justify-content:space-between;align-items:center;margin-top:16px;}
  /* Quiz */
  .quiz-q{font-family:'Zilla Slab',serif;font-size:1.1rem;margin:10px 0 16px;line-height:1.4;}
  .choice{
    display:block;width:100%;text-align:left;
    border:2px solid var(--ink);background:var(--paper);
    padding:11px 14px;margin-bottom:8px;border-radius:var(--radius);
    font-family:'Inter',sans-serif;font-size:0.92rem;cursor:pointer;
    touch-action:manipulation;overflow-wrap:break-word;
  }
  .choice:hover:not(:disabled){background:var(--paper-dark);}
  .choice.correct{background:var(--stamp-green);color:var(--paper);border-color:var(--stamp-green);}
  .choice.incorrect{background:var(--stamp-red);color:var(--paper);border-color:var(--stamp-red);}
  .choice:disabled{cursor:default;}
  .exp-box{background:var(--paper-dark);border-left:4px solid var(--brass);padding:12px 16px;margin-top:12px;font-size:0.88rem;line-height:1.5;display:none;}
  .exp-box.show{display:block;}
  .scorebar{font-family:'IBM Plex Mono',monospace;font-size:0.8rem;color:var(--ink-soft);margin-bottom:6px;}
  /* Exam */
  .exam-header{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:8px;margin-bottom:12px;}
  .timer{font-family:'IBM Plex Mono',monospace;font-size:1.1rem;font-weight:600;background:var(--ink);color:var(--paper);padding:6px 14px;border-radius:var(--radius);}
  .timer.low{background:var(--stamp-red);}
  .results-grid{display:grid;grid-template-columns:1fr auto;gap:6px 16px;font-family:'IBM Plex Mono',monospace;font-size:0.85rem;margin:16px 0;}
  .results-grid .barwrap{grid-column:1/-1;background:var(--paper-dark);border-radius:2px;height:8px;overflow:hidden;margin-bottom:8px;}
  .results-grid .bar{height:100%;background:var(--stamp-green);}
  /* Progress */
  .stat-row{display:flex;gap:16px;flex-wrap:wrap;margin-bottom:20px;}
  .stat-box{border:2px solid var(--ink);border-radius:var(--radius);padding:14px 18px;flex:1;min-width:140px;text-align:center;}
  .stat-box .num{font-family:'Zilla Slab',serif;font-size:1.8rem;font-weight:700;}
  .stat-box .lbl{font-family:'IBM Plex Mono',monospace;font-size:0.68rem;text-transform:uppercase;color:var(--ink-soft);letter-spacing:0.04em;}
  ul.missed-list{list-style:none;padding:0;margin:0;}
  ul.missed-list li{border-bottom:1px solid var(--paper-dark);padding:10px 4px;display:flex;justify-content:space-between;align-items:center;gap:10px;font-size:0.88rem;overflow-wrap:break-word;}
  @media (max-width:600px){
    body{padding:14px 10px 40px;}
    .sheet{max-width:100%;}
    .titleblock{flex-direction:column;align-items:flex-start;padding:14px 16px;margin-bottom:16px;}
    .titleblock h1{font-size:1.3rem;}
    .titleblock .sub{font-size:0.68rem;}
    .tb-meta{text-align:left;font-size:0.68rem;}
    main{padding:18px 14px;min-height:auto;}
    h2.section-title{font-size:1.15rem;}
    nav.tabs{
      flex-wrap:nowrap;
      overflow-x:auto;
      -webkit-overflow-scrolling:touch;
      scrollbar-width:none;
      margin:0 -10px 16px;
      padding:0 10px 6px;
    }
    nav.tabs::-webkit-scrollbar{display:none;}
    nav.tabs button{flex:0 0 auto;padding:10px 14px;font-size:0.68rem;}
    .card-scene{height:280px;max-width:100%;}
    .face{padding:18px;}
    .face .txt{font-size:1.05rem;}
    .face.back .txt{font-size:0.9rem;}
    .quiz-q{font-size:1rem;overflow-wrap:break-word;}
    .flash-controls{gap:8px;}
    button.btn{padding:11px 14px;font-size:0.82rem;}
    .choice{padding:12px 14px;font-size:0.88rem;}
    .prob-card{padding:16px;}
    .stat-row{gap:10px;}
    .stat-box{min-width:calc(50% - 5px);padding:12px 10px;}
    .stat-box .num{font-size:1.5rem;}
    .results-grid{font-size:0.76rem;gap:5px 10px;}
    .exam-header{gap:10px;}
    .timer{font-size:1rem;padding:6px 12px;}
    ul.missed-list li{font-size:0.82rem;}
    .nav-row{flex-wrap:wrap;gap:8px;}
  }
  @media (max-width:380px){
    .titleblock h1{font-size:1.15rem;}
    .card-scene{height:260px;}
    .stat-box{min-width:100%;}
  }
  @media (prefers-reduced-motion: reduce){
    .flashcard{transition:none;}
  }

  /* SRS badges + empty-deck state */
  .srs-badge{
    display:inline-block;font-family:'IBM Plex Mono',monospace;font-size:0.65rem;
    text-transform:uppercase;letter-spacing:0.05em;padding:3px 8px;border-radius:2px;
    background:var(--paper-dark);color:var(--ink-soft);border:1px solid var(--ink-soft);
  }
  .srs-badge.due-now{background:var(--brass);color:var(--ink);border-color:var(--brass-dark);}
  .srs-badge.mastered{background:var(--stamp-green);color:var(--paper);border-color:var(--stamp-green);}
  .empty-state{
    border:2px dashed var(--ink-soft);border-radius:6px;padding:32px 20px;
    text-align:center;color:var(--ink-soft);
  }
  .empty-state .big{font-family:'Zilla Slab',serif;font-size:1.3rem;color:var(--ink);margin-bottom:8px;}

  /* Quiz category picker */
  .select-input{
    font-family:'Inter',sans-serif;font-size:0.9rem;padding:10px 12px;
    border:2px solid var(--ink);border-radius:var(--radius);background:var(--paper);
    color:var(--ink);width:100%;max-width:340px;margin-bottom:14px;
  }

  /* Offline banner */
  #offlineBanner{
    position:fixed;bottom:0;left:0;right:0;z-index:999;
    background:var(--stamp-red);color:var(--paper);
    font-family:'IBM Plex Mono',monospace;font-size:0.78rem;
    text-align:center;padding:8px 12px;
    padding-bottom:calc(8px + env(safe-area-inset-bottom));
  }

  /* Export/Import row */
  .io-row{display:flex;gap:10px;flex-wrap:wrap;margin-top:10px;}