:root{
    --bg: #1C231F;
    --panel: #232B26;
    --panel-2: #2A332D;
    --line: #3A453D;
    --text: #EFEBDE;
    --muted: #A9B3A5;
    --yellow: #E8B84B;
    --teal: #7FC4A6;
    --red: #E8896B;
    --code-bg: #141815;
  }
  *{ box-sizing: border-box; }
  html{ scroll-behavior: smooth; }
  body{
    margin:0;
    background: var(--bg);
    color: var(--text);
    font-family: 'Inter', system-ui, sans-serif;
    line-height: 1.65;
    -webkit-font-smoothing: antialiased;
  }
  .wrap{
    max-width: 720px;
    margin: 0 auto;
    padding: 0 24px 120px;
  }
  h1, h2, h3{
    font-family: 'Fraunces', Georgia, serif;
    font-weight: 600;
    line-height: 1.15;
    margin: 0 0 14px;
  }
  h2{ font-size: 1.7rem; }
  h3{ font-size: 1.15rem; color: var(--teal); font-weight: 500; }
  p{ margin: 0 0 16px; color: var(--text); }
  .muted{ color: var(--muted); }
  a{ color: var(--yellow); }
  .course-nav{ padding-top: 24px; font-size: 0.9rem; }
  .course-nav a{ display: inline-flex; align-items: center; gap: 8px; text-decoration: none; }
  .course-nav a:hover{ text-decoration: underline; }

  /* Hero */
  .hero{
    padding: 90px 0 50px;
    animation: rise 0.7s ease-out both;
  }
  @keyframes rise{
    from{ opacity: 0; transform: translateY(10px); }
    to{ opacity: 1; transform: translateY(0); }
  }
  .hero .kicker{
    color: var(--muted);
    font-size: 0.95rem;
    margin-bottom: 10px;
  }
  .hero h1{
    font-size: clamp(2.2rem, 6vw, 3.2rem);
    font-style: italic;
    font-weight: 340;
  }
  .hero .squiggle{ width: 140px; height: 14px; margin: 18px 0 22px; display:block; }
  .hero p.lead{
    font-size: 1.1rem;
    color: var(--text);
    max-width: 54ch;
  }
  .hero .meta{ color: var(--muted); font-size: 0.95rem; }

  /* Steps */
  .step{
    padding: 46px 0;
    border-top: 1px solid var(--line);
  }
  .step-head{
    display: flex;
    align-items: baseline;
    gap: 16px;
    margin-bottom: 18px;
  }
  .badge{
    flex: none;
    width: 34px; height: 34px;
    border-radius: 50%;
    border: 1.5px solid var(--yellow);
    color: var(--yellow);
    display: flex; align-items: center; justify-content: center;
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.9rem;
  }

  /* Code blocks */
  pre{
    background: var(--code-bg);
    border: 1px solid var(--line);
    border-radius: 10px;
    padding: 16px 18px;
    overflow-x: auto;
    margin: 0 0 12px;
  }
  code{
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.88rem;
    color: #C9E8CE;
  }
  .kw{ color: var(--yellow); }
  .fn{ color: #8FCBEB; }
  .cm{ color: var(--muted); font-style: italic; }
  .str{ color: #E3B778; }

  .callout{
    background: var(--panel);
    border: 1px solid var(--line);
    border-left: 3px solid var(--teal);
    border-radius: 8px;
    padding: 14px 18px;
    margin: 16px 0;
    font-size: 0.95rem;
  }
  .callout.warn{ border-left-color: var(--red); }
  .callout strong{ color: var(--teal); }
  .callout.warn strong{ color: var(--red); }

  /* Try it */
  .tryit{
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: 10px;
    padding: 16px 18px;
    margin: 18px 0;
  }
  .tryit-row{ display:flex; align-items:center; gap: 12px; margin-bottom: 8px; flex-wrap: wrap;}
  .tryit-label{ font-size: 0.85rem; color: var(--muted); }
  button.run{
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.85rem;
    background: transparent;
    color: var(--yellow);
    border: 1px solid var(--yellow);
    border-radius: 6px;
    padding: 7px 14px;
    cursor: pointer;
    transition: background 0.15s ease, color 0.15s ease;
  }
  button.run:hover{ background: var(--yellow); color: #141815; }
  .output{
    font-family: 'JetBrains Mono', monospace;
    font-size: 0.9rem;
    color: var(--teal);
    padding: 8px 0 0;
    min-height: 1.3em;
  }

  /* Calculator demo */
  .calc{
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: 14px;
    padding: 24px;
    margin-top: 10px;
  }
  .calc-inputs{
    display: flex;
    gap: 12px;
    margin-bottom: 16px;
    align-items: center;
    flex-wrap: wrap;
  }
  .calc-inputs input{
    flex: 1;
    min-width: 90px;
    background: var(--code-bg);
    border: 1px solid var(--line);
    color: var(--text);
    font-family: 'JetBrains Mono', monospace;
    font-size: 1.1rem;
    padding: 10px 12px;
    border-radius: 8px;
  }
  .calc-inputs input:focus{ outline: 1.5px solid var(--teal); }
  .op-row{
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin-bottom: 18px;
  }
  .op-row button{
    font-family: 'JetBrains Mono', monospace;
    font-size: 1.2rem;
    background: var(--panel-2);
    border: 1px solid var(--line);
    color: var(--text);
    border-radius: 8px;
    padding: 12px 0;
    cursor: pointer;
    transition: border-color 0.15s ease, color 0.15s ease;
  }
  .op-row button:hover{ border-color: var(--yellow); color: var(--yellow); }
  .calc-result{
    background: var(--code-bg);
    border: 1px solid var(--line);
    border-radius: 8px;
    padding: 16px;
    font-family: 'JetBrains Mono', monospace;
    font-size: 1.05rem;
    color: var(--teal);
    min-height: 1.4em;
  }
  .calc-result .err{ color: var(--red); }
  details{ margin-top: 14px; }
  summary{
    cursor: pointer;
    color: var(--muted);
    font-size: 0.9rem;
    margin-bottom: 10px;
  }

  .recap-list{ list-style: none; margin: 0; padding: 0; }
  .recap-list li{
    padding: 10px 0;
    border-top: 1px solid var(--line);
    display: flex; gap: 14px;
  }
  .recap-list li:first-child{ border-top: none; }
  .recap-list code{ color: var(--yellow); flex: none; }
  .next-step{ margin-top: 22px; }

  footer{
    padding: 40px 0 10px;
    color: var(--muted);
    font-size: 0.85rem;
    border-top: 1px solid var(--line);
    margin-top: 20px;
  }

  @media (prefers-reduced-motion: reduce){
    .hero{ animation: none; }
    html{ scroll-behavior: auto; }
  }

  .calc-form{ background:var(--panel); border:1px solid var(--line); border-radius:14px; padding:24px; margin-top:10px; }
  .form-grid{ display:grid; grid-template-columns:repeat(3,1fr); gap:12px; margin-bottom:16px; }
  .form-grid label{ color:var(--muted); font-size:.85rem; }
  .form-grid input,.form-grid select{ display:block; width:100%; margin-top:6px; background:var(--code-bg); border:1px solid var(--line); color:var(--text); font:inherit; padding:10px 12px; border-radius:8px; }
  .form-grid input:focus,.form-grid select:focus { outline:1.5px solid var(--teal); }
  .form-submit{ background:var(--yellow); border:1px solid var(--yellow); border-radius:7px; color:#141815; cursor:pointer; font:600 .9rem 'JetBrains Mono',monospace; padding:10px 15px; }
  .form-status { color:var(--teal); font-family:'JetBrains Mono', monospace; margin:14px 0 0; min-height:1.5em; }
  .form-status.err { color:var(--red); }
  @media (max-width:620px){ .form-grid { grid-template-columns:1fr; } }