*{margin:0;padding:0;box-sizing:border-box}
        :root{
            --bg:#fff;--text:#333;--muted:#999;--light:#b5b5b5;--line:#e5e5e5;--dark:#1a1a1a;
            --blue:#2a6cb6;--blue-bg:#f0f5fb;
            --teal:#1a7a5a;--teal-bg:#edf7f2;
            --amber:#8a5a10;--amber-bg:#fdf5e6;
            --coral:#a04020;--coral-bg:#fdf0eb;
            --purple:#6b46a8;--purple-bg:#f4f0fa
        }
        ::selection{background:#d5d5d5;color:var(--dark)}
        html{-webkit-text-size-adjust:100%;scroll-behavior:smooth}
        body{font-family:'Source Serif 4',Georgia,serif;background:var(--bg);color:var(--text);line-height:1.75;font-size:17px;-webkit-font-smoothing:antialiased}
        .layout{display:flex;min-height:100vh;max-width:1060px;margin:0 auto;padding:56px 32px 56px 0}
        nav{position:sticky;top:56px;align-self:flex-start;min-width:150px;padding:0 36px 0 32px;text-align:right}
        nav a{display:block;font-family:'Inter',sans-serif;font-size:14px;color:var(--muted);text-decoration:none;padding:4px 0;transition:color .2s}
        nav a:hover{color:var(--dark)}
        nav a.active{color:var(--dark);font-weight:500;text-decoration:underline;text-underline-offset:4px;text-decoration-thickness:1px}
        .divider{width:1px;background:var(--line);flex-shrink:0}
        main{flex:1;padding-left:48px;max-width:700px}
        .page-label{font-family:'Inter',sans-serif;font-size:13px;color:var(--light);margin-bottom:2px}
        .page-name{font-size:22px;font-weight:400;color:var(--dark);margin-bottom:28px}
        h2{font-size:17px;font-weight:600;color:var(--dark);margin:36px 0 12px}
        p{margin-bottom:16px;line-height:1.8}

        .formula-block{background:var(--blue-bg);border-left:3px solid var(--blue);padding:14px 18px;margin:18px 0}
        .formula-block .f-label{font-family:'Inter',sans-serif;font-size:10px;text-transform:uppercase;letter-spacing:.08em;color:var(--blue);margin-bottom:6px}
        .formula-block .f-expr{font-family:'Source Serif 4',serif;font-style:italic;font-size:15px;color:var(--dark);line-height:1.8}
        .formula-block .f-note{font-family:'Inter',sans-serif;font-size:11px;color:var(--muted);margin-top:6px;line-height:1.5}
        .f-var{color:var(--blue);font-style:italic}
        .key-point{border-left:3px solid var(--blue);padding:10px 16px;margin:20px 0;font-size:15px;background:var(--blue-bg);color:#1a4a7a;font-family:'Inter',sans-serif;line-height:1.6}

        /* three-curve legend */
        .curve-legend{display:flex;gap:20px;margin:14px 0;flex-wrap:wrap}
        .curve-leg-item{display:flex;align-items:center;gap:7px;font-family:'Inter',sans-serif;font-size:12px;color:var(--muted)}
        .leg-line{width:28px;height:2px}
        .leg-line.dashed{background:repeating-linear-gradient(90deg,#7a9bc2 0,#7a9bc2 5px,transparent 5px,transparent 9px)}

        /* module box */
        .module-box{border:1px solid var(--line);margin:32px 0;padding:0}
        .module-header{padding:14px 18px;border-bottom:1px solid var(--line);background:#fafafa;display:flex;align-items:center;justify-content:space-between;flex-wrap:wrap;gap:8px}
        .module-title-inner{font-family:'Inter',sans-serif;font-size:12px;font-weight:600;color:var(--dark);text-transform:uppercase;letter-spacing:.06em}
        .tab-group{display:flex;gap:4px}
        .tab-btn{font-family:'Inter',sans-serif;font-size:11px;padding:4px 12px;border:1px solid var(--line);background:#fff;color:var(--muted);cursor:pointer;transition:all .15s}
        .tab-btn.active{background:var(--blue);border-color:var(--blue);color:#fff}
        .module-body-inner{padding:20px 18px}

        /* shape preset buttons */
        .shape-group{display:flex;gap:5px;margin-bottom:16px;flex-wrap:wrap}
        .shape-btn{font-family:'Inter',sans-serif;font-size:11px;padding:5px 14px;border:1px solid var(--line);background:#fff;color:var(--muted);cursor:pointer;transition:all .15s}
        .shape-btn.active{background:var(--blue);border-color:var(--blue);color:#fff}

        /* controls */
        .controls-row{display:grid;grid-template-columns:1fr 1fr 1fr;gap:16px;margin-bottom:14px}
        .ctrl-group{display:flex;flex-direction:column;gap:5px}
        .ctrl-label{font-family:'Inter',sans-serif;font-size:10px;color:var(--muted);text-transform:uppercase;letter-spacing:.06em}
        .ctrl-value{font-family:'Inter',sans-serif;font-size:13px;font-weight:600;color:var(--dark)}
        input[type=range]{width:100%;accent-color:var(--blue);height:3px;cursor:pointer}

        .canvas-wrap{background:#fafafa;border:1px solid var(--line);margin-bottom:10px}
        canvas{display:block}

        /* shape info box */
        .shape-info{font-family:'Inter',sans-serif;font-size:12px;padding:10px 14px;margin-bottom:4px;min-height:48px;line-height:1.6;border-left:3px solid transparent}
        .shape-info.normal{border-color:var(--blue);background:var(--blue-bg);color:#1a4a7a}
        .shape-info.inverted{border-color:var(--coral);background:var(--coral-bg);color:#6a2010}
        .shape-info.flat{border-color:var(--amber);background:var(--amber-bg);color:#5a3a08}
        .shape-info.humped{border-color:var(--purple);background:var(--purple-bg);color:#4a2880}

        /* bootstrap controls */
        .par-grid{display:grid;grid-template-columns:repeat(5,1fr);gap:10px;margin-bottom:14px}
        .par-ctrl{display:flex;flex-direction:column;gap:4px;align-items:center}
        .par-ctrl .ctrl-label{text-align:center}
        .par-ctrl .ctrl-value{text-align:center;font-size:13px}
        .par-ctrl input{accent-color:var(--blue)}

        /* step controls */
        .step-row{display:flex;align-items:center;gap:8px;margin-bottom:14px;flex-wrap:wrap}
        .step-label{font-family:'Inter',sans-serif;font-size:11px;color:var(--muted);text-transform:uppercase;letter-spacing:.06em}
        .step-btn{font-family:'Inter',sans-serif;font-size:11px;padding:5px 12px;border:1px solid var(--line);background:#fff;color:var(--muted);cursor:pointer;transition:all .15s;min-width:38px;text-align:center}
        .step-btn.active{background:var(--blue);border-color:var(--blue);color:#fff}
        .step-btn.done{border-color:rgba(42,108,182,.4);color:var(--blue);background:var(--blue-bg)}

        /* bootstrap formula box */
        .bs-formula{font-family:'Inter',sans-serif;font-size:12px;padding:12px 14px;background:#fafafa;border:1px solid var(--line);min-height:56px;line-height:1.7;color:var(--text)}
        .bs-formula strong{color:var(--blue)}
        .bs-formula .bs-result{font-size:14px;font-weight:600;color:var(--teal);margin-top:4px}

        /* relationship table */
        table.rel{width:100%;border-collapse:collapse;font-family:'Inter',sans-serif;font-size:13px;margin:16px 0}
        table.rel th{background:var(--blue-bg);color:var(--blue);font-weight:600;padding:8px 12px;text-align:left;border-bottom:2px solid var(--blue);font-size:11px;text-transform:uppercase;letter-spacing:.06em}
        table.rel td{padding:8px 12px;border-bottom:1px solid var(--line);vertical-align:top}
        table.rel tr:last-child td{border-bottom:none}

        .module-nav{display:flex;justify-content:space-between;align-items:center;margin-top:48px;padding-top:20px;border-top:1px solid var(--line)}
        .nav-prev,.nav-next{font-family:'Inter',sans-serif;font-size:13px;text-decoration:none}
        .nav-prev{color:var(--muted)}.nav-prev:hover{color:var(--dark)}
        .nav-next{color:var(--blue)}.nav-next:hover{color:var(--dark)}
        .footer{margin-top:44px;padding-top:18px;border-top:1px solid var(--line);font-family:'Inter',sans-serif;font-size:12px;color:var(--light)}

        @media(max-width:768px){
            .layout{flex-direction:column;padding:28px 20px}
            nav{position:static;text-align:left;min-width:auto;padding:0 0 24px 0;display:flex;flex-wrap:wrap;gap:3px 14px}
            nav a{display:inline}.divider{width:100%;height:1px}
            main{padding-left:0;padding-top:28px;max-width:100%}
            .controls-row,.par-grid{grid-template-columns:1fr 1fr}
        }
    
        .skip-link{position:absolute;left:-9999px;top:8px;background:var(--dark);color:#fff;padding:8px 12px;z-index:10;font-family:'Inter',sans-serif}
        .skip-link:focus{left:8px}
        .learning-goals{border-left:3px solid var(--teal);background:var(--teal-bg);padding:14px 18px;margin:0 0 28px;font-family:'Inter',sans-serif;font-size:13px;line-height:1.65}
        .learning-goals strong,.assumption-note strong,.source-note strong{color:var(--dark)}
        .learning-goals ul{margin:6px 0 0 18px}
        .assumption-note{border-left:3px solid var(--amber);background:var(--amber-bg);padding:12px 16px;margin:18px 0 26px;font-family:'Inter',sans-serif;font-size:13px;line-height:1.65;color:var(--text)}
        .source-note{border-top:1px solid var(--line);padding-top:16px;margin-top:34px;font-family:'Inter',sans-serif;font-size:12px;line-height:1.65;color:var(--muted)}
        .source-note a{color:var(--blue);text-underline-offset:2px}
        canvas{max-width:100%;height:auto}
        button:focus-visible,input:focus-visible,a:focus-visible{outline:2px solid var(--blue);outline-offset:3px}
        @media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*::before,*::after{animation-duration:.01ms!important;animation-iteration-count:1!important;transition-duration:.01ms!important}}