:root{
  --paper:#EFE7D3;
  --paper-2:#F7F1E3;
  --ink:#16323C;
  --ink-soft:#5D6B6A;
  --rust:#B5432A;
  --aqua:#2E7D8C;
  --line:#C9BFA6;
}
*{margin:0;padding:0;box-sizing:border-box;-webkit-tap-highlight-color:transparent}
html,body{background:var(--paper);color:var(--ink);
  font-family:'IBM Plex Mono',monospace;-webkit-font-smoothing:antialiased}

/* Hide scrollbars visually but retain scroll functionality */
::-webkit-scrollbar { display: none; }
* { -ms-overflow-style: none; scrollbar-width: none; }

/* ---------- masthead ---------- */
#masthead{display:flex;align-items:center;gap:12px;padding:12px 16px;
  background:var(--paper);border-bottom:1px solid var(--line)}
#masthead .crest{width:34px;height:34px;border:2px solid var(--ink);border-radius:6px;
  display:flex;align-items:center;justify-content:center;font-size:16px;flex:none}
#masthead .mast-title{flex:1;text-align:center}
#masthead .kick{font-family:Georgia,serif;font-style:italic;font-size:11px;
  letter-spacing:.28em;text-transform:uppercase;color:var(--rust)}
#masthead h1{font-family:Georgia,'Times New Roman',serif;font-weight:700;
  font-size:18px;line-height:1.25}

/* ---------- 3D viewport ---------- */
#viewport{position:relative;height:56vh;min-height:300px;background:#0B1D26;overflow:hidden}
#scene{position:absolute;inset:0;width:100%;height:100%;touch-action:none;display:block}
.cross{position:absolute;color:rgba(127,209,201,.5);font-size:26px;line-height:1;
  pointer-events:none;font-family:'IBM Plex Mono',monospace}
.cross.tl{top:8px;left:12px}.cross.tr{top:8px;right:12px}
.cross.bl{bottom:8px;left:12px}.cross.br{bottom:8px;right:12px}
#hudCard{position:absolute;top:14px;left:14px;width:180px;
  background:rgba(74,90,99,.92);color:#EDF2F1;border-radius:4px;
  padding:12px 14px;box-shadow:0 4px 16px rgba(0,0,0,.45)}
#hudCard label{display:block;font-size:9px;letter-spacing:.2em;text-transform:uppercase;
  color:#B9C6C4;margin-bottom:3px}
#hudCard b{display:block;font-size:19px;font-weight:600;margin-bottom:7px}
#hudCard b.sm{font-size:15px;margin-bottom:0}
#hudCard .bar{height:4px;background:rgba(255,255,255,.25);border-radius:2px;
  overflow:hidden;margin-bottom:11px}
#hudCard .bar i{display:block;height:100%;background:#63d08e;width:0%}
#caption{position:absolute;bottom:12px;right:12px;background:rgba(35,46,53,.9);
  color:#DFE7E5;font-size:9.5px;letter-spacing:.18em;text-transform:uppercase;
  padding:6px 11px;border-radius:3px;pointer-events:none}
#valve{position:absolute;top:14px;right:14px;padding:5px 9px;border:1px solid #E8B44A;
  color:#E8B44A;font-size:9px;letter-spacing:.12em;text-transform:uppercase;
  background:rgba(11,29,38,.8);opacity:0;transition:opacity .3s;pointer-events:none;
  display:flex;align-items:center;gap:7px;border-radius:3px}
#valve .dot{width:7px;height:7px;border-radius:50%;background:#E8B44A;animation:blink 1s infinite}
@keyframes blink{50%{opacity:.2}}
#hint{position:absolute;bottom:10px;left:0;right:0;text-align:center;font-size:8.5px;
  color:rgba(242,234,217,.55);letter-spacing:.12em;text-transform:uppercase;
  pointer-events:none;transition:opacity 1s}
.flabel{position:absolute;z-index:3;transform:translate(-50%,-160%);
  padding:3px 9px;border-radius:5px;font-size:11px;font-weight:700;letter-spacing:.05em;
  pointer-events:none;transition:opacity .2s;box-shadow:0 3px 8px rgba(0,0,0,.35)}
.flabel.l{background:#3f9fc4;color:#052330}
.flabel.r{background:#e0a23c;color:#3a2600}

/* ---------- instrument panel ---------- */
#panel{padding:20px 16px 40px;max-width:780px;margin:0 auto}
#panel h2{font-family:Georgia,'Times New Roman',serif;font-size:28px;font-weight:700;
  margin-bottom:4px}
#panel .lede{color:var(--ink-soft);font-size:12.5px;line-height:1.5;margin-bottom:16px;
  font-family:Georgia,serif;font-style:italic}

/* ---------- beginner-friendly explainer ---------- */
.introcard{background:var(--paper-2);border:1px solid var(--line);border-left:4px solid var(--aqua);
  border-radius:4px;padding:12px 14px;font-size:12.5px;line-height:1.65;margin-bottom:20px;color:var(--ink)}
.introcard b{color:var(--aqua)}

/* ---------- live letter strip ---------- */
#stripwrap{margin-bottom:20px}
.tiles{display:flex;gap:3px;flex-wrap:nowrap;justify-content:center;background:var(--paper-2);
  border:1px solid var(--line);border-radius:8px;padding:16px 8px;overflow-x:auto}
.tile{display:flex;flex-direction:column;align-items:center;justify-content:center;
  width:28px;height:36px;border-radius:6px;background:#3a4a52;color:#d7dee1;flex:none;
  font-family:'IBM Plex Mono',monospace;transition:background .25s ease,transform .25s ease,color .25s ease}
.tile .ch{font-size:15px;font-weight:700;line-height:1}
.tile .idx{font-size:8px;opacity:.65;margin-top:2px}
.tile.l{background:#3f9fc4;color:#052330;transform:translateY(-5px)}
.tile.r{background:#e0a23c;color:#3a2600;transform:translateY(-5px)}
.tile.done{background:#4f9d7a;color:#052318}

#controls{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:22px}
.tab{font-family:Georgia,serif;font-style:italic;font-size:14px;
  background:var(--paper-2);color:var(--ink);border:1px solid var(--line);
  padding:9px 14px;cursor:pointer;border-radius:2px;flex:1 1 28%;min-width:0}
.tab:active{transform:translateY(1px)}
.tab.active{background:var(--rust);border-color:var(--rust);color:var(--paper-2);
  font-weight:700;font-style:normal}

.kicker{font-size:11px;letter-spacing:.28em;text-transform:uppercase;color:var(--rust);
  font-weight:600;margin:20px 0 10px}

#stepline{display:flex;align-items:center;gap:10px;margin-bottom:6px}
#stepnum{font-size:11px;letter-spacing:.14em;text-transform:uppercase;color:var(--ink-soft);
  white-space:nowrap;font-weight:600}
#progress{flex:1;height:4px;background:#DCD2B8;position:relative;overflow:hidden;border-radius:2px}
#progress i{position:absolute;inset:0;right:auto;background:var(--rust);width:0%}
#steplabel{font-family:Georgia,serif;font-size:20px;font-weight:700;margin:4px 0 8px}
#stepdesc{font-size:13px;line-height:1.65;color:var(--ink)}
#fact{margin-top:12px;padding:10px 12px;border-left:4px solid var(--rust);
  background:var(--paper-2);font-size:12px;line-height:1.55;color:#4a4437}
#fact b{color:var(--rust)}
/* ---------- code editor panel ---------- */
#codepanel{margin-top:14px;background:#0d1117;border:1px solid #232b36;border-radius:10px;
  overflow:hidden;box-shadow:0 14px 34px -16px rgba(0,0,0,.55)}
#codepanel .ed-head{padding:9px 14px;border-bottom:1px solid #232b36;
  display:flex;align-items:center;gap:7px;font-size:10.5px;color:#7d8894}
#codepanel .ed-dot{width:9px;height:9px;border-radius:50%}
#codepanel .ed-dot.r{background:#ff5f56}#codepanel .ed-dot.y{background:#ffbd2e}#codepanel .ed-dot.g{background:#27c93f}
#codepanel .ed-file{margin-left:6px}
#codepanel pre{margin:0;padding:10px 0;font-size:13px;line-height:1.75;overflow-x:auto}
#codepanel .cline{display:flex;padding:0 16px;border-left:3px solid transparent}
#codepanel .cline.active{background:rgba(52,211,153,.10);border-left-color:#34d399}
#codepanel .cln{width:20px;color:#3d4a5a;user-select:none;flex-shrink:0}
#codepanel .ccode{white-space:pre}
#codepanel .kw{color:#ff7b72}#codepanel .fn{color:#79c0ff}
#codepanel .num{color:#79c0ff}#codepanel .op{color:#ff9d5c}#codepanel .pl{color:#e6edf3}#codepanel .str{color:#a5d6ff}
#plainLine{padding:10px 14px;border-top:1px solid #232b36;font-size:11.5px;line-height:1.55;
  color:#9fb0bd;font-family:Georgia,serif;font-style:italic;background:#0d1117}
#plainLine b{color:#e6edf3;font-style:normal}
footer{margin-top:28px;font-size:10px;letter-spacing:.2em;text-transform:uppercase;
  color:var(--ink-soft);text-align:center}

/* ---------- mobile: keep the simulation pinned while the panel scrolls ---------- */
@media (max-width:899px){
  #viewport{position:sticky; top:0; z-index:20; height: 45vh; min-height: 250px;}
  #masthead h1{font-size: 15px;}
  #masthead .kick{font-size: 9px;}
  #hudCard{transform: scale(0.85); transform-origin: top left;}
  #caption{transform: scale(0.8); transform-origin: bottom right; bottom: 25px;}
  #hint{font-size: 7px; bottom: 6px; padding: 0 10px;}
}

/* ---------- large screens: full-height 3D + fixed right sidebar ---------- */
@media (min-width:900px){
  html,body{height:100%;overflow:hidden}
  body{display:grid;grid-template-columns:1fr 400px;grid-template-rows:auto 1fr}
  #masthead{grid-column:1/3}
  #viewport{grid-column:1;grid-row:2;height:auto;min-height:0}
  #panel{grid-column:2;grid-row:2;overflow-y:auto;max-width:none;margin:0;
    border-left:1px solid var(--line);padding:18px 20px 48px;background:var(--paper)}
  #panel h2{font-size:22px}
  #panel .lede{font-size:11.5px;margin-bottom:12px}
  .tab{flex:1 1 30%;font-size:13px;padding:8px 8px}
  #hudCard{width:200px}
}
@media (min-width:1500px){
  body{grid-template-columns:1fr 460px}
}