:root {
            --primary: #2563eb;
            --primary-light: #60a5fa;
            --primary-dark: #1d4ed8;
            --purple: #7c3aed;
            --cyan: #06b6d4;
            --emerald: #10b981;
            --text: #1e293b;
            --text-sec: #64748b;
            --text-light: #94a3b8;
            --bg: #f8fafc;
            --bg2: #f1f5f9;
            --bg3: #e2e8f0;
            --card: #ffffff;
            --border: #e2e8f0;
            --success: #22c55e;
            --warning: #f59e0b;
            --error: #ef4444;
            --shadow: 0 4px 6px -1px rgb(0 0 0/.1),0 2px 4px -2px rgb(0 0 0/.1);
            --shadow-lg: 0 10px 15px -3px rgb(0 0 0/.1),0 4px 6px -4px rgb(0 0 0/.1);
            --shadow-xl: 0 20px 25px -5px rgb(0 0 0/.1),0 8px 10px -6px rgb(0 0 0/.1);
        }
        *{box-sizing:border-box;margin:0;padding:0}
        html{scroll-behavior:smooth}
        body{font-family:'Inter',system-ui,sans-serif;line-height:1.7;color:var(--text);background:linear-gradient(135deg,#f8fafc 0%,#e2e8f0 100%);min-height:100vh;-webkit-font-smoothing:antialiased}

        /* NAV */
        .nav{position:sticky;top:0;z-index:100;background:rgba(255,255,255,.92);backdrop-filter:blur(12px);border-bottom:1px solid var(--border);padding:.75rem 2rem;display:flex;align-items:center;gap:1.5rem;flex-wrap:wrap}
        .nav-brand{font-weight:700;font-size:1.1rem;background:linear-gradient(135deg,var(--primary),var(--purple));-webkit-background-clip:text;-webkit-text-fill-color:transparent;white-space:nowrap}
        .nav-links{display:flex;gap:.5rem;flex-wrap:wrap}
        .nav-links a{text-decoration:none;color:var(--text-sec);font-size:.85rem;font-weight:500;padding:.35rem .75rem;border-radius:8px;transition:all .2s}
        .nav-links a:hover{background:var(--bg2);color:var(--primary)}

        .container{max-width:1100px;margin:0 auto;padding:1.5rem}

        /* HERO */
        .hero{text-align:center;padding:3rem 1rem 2rem;position:relative}
        .hero h1{font-size:clamp(2.2rem,5vw,3.5rem);font-weight:800;background:linear-gradient(135deg,var(--primary),var(--purple));-webkit-background-clip:text;-webkit-text-fill-color:transparent;margin-bottom:.75rem}
        .hero p{font-size:1.15rem;color:var(--text-sec);max-width:640px;margin:0 auto}

        /* CARDS */
        .card{background:var(--card);border-radius:20px;box-shadow:var(--shadow-lg);margin-bottom:2rem;overflow:hidden;border:1px solid var(--border);transition:box-shadow .3s}
        .card:hover{box-shadow:var(--shadow-xl)}
        .card-hdr{padding:1.75rem 2rem;color:#fff;position:relative;overflow:hidden}
        .card-hdr.light{background:linear-gradient(135deg,#2563eb,#60a5fa)}
        .card-hdr.sound{background:linear-gradient(135deg,#7c3aed,#a78bfa)}
        .card-hdr.wave{background:linear-gradient(135deg,#0891b2,#22d3ee)}
        .card-hdr.quiz{background:linear-gradient(135deg,#dc2626,#f87171)}
        .card-hdr h1{font-size:1.75rem;font-weight:700;position:relative;z-index:1}
        .card-body{padding:2rem}

        /* HEADINGS */
        h2{font-size:1.75rem;font-weight:700;color:var(--primary);margin-bottom:1.25rem;padding-left:1rem;position:relative}
        h2::before{content:'';position:absolute;left:0;top:50%;transform:translateY(-50%);width:4px;height:1.75rem;background:linear-gradient(180deg,var(--primary),var(--primary-light));border-radius:2px}
        h3{font-size:1.35rem;font-weight:600;color:var(--primary-dark);margin:2rem 0 1rem}
        h4{font-size:1.15rem;font-weight:600;color:var(--text);margin:1.25rem 0 .75rem}
        p{margin-bottom:.75rem}
        ul,ol{padding-left:1.5rem;margin-bottom:.75rem}
        li{margin-bottom:.4rem}

        .divider{height:1px;background:linear-gradient(90deg,transparent,var(--border),transparent);margin:2rem 0}

        /* KEY TERMS */
        .term{font-weight:600;color:var(--primary-dark);background:rgba(37,99,235,.08);padding:.1rem .4rem;border-radius:4px}

        /* LEARNING OUTCOMES */
        .outcomes{background:linear-gradient(135deg,#faf5ff,#f3e8ff);border:2px solid #d8b4fe;border-radius:14px;padding:1.25rem 1.5rem;margin:1.25rem 0;position:relative}
        .outcomes h4{color:var(--purple);margin-top:0}
        .outcomes ul{margin:0;padding-left:1.25rem}
        .outcomes li{margin-bottom:.35rem}

        /* FORMULAS */
        .formula{background:linear-gradient(135deg,#eff6ff,#dbeafe);border:2px solid var(--primary-light);border-radius:14px;padding:1.25rem;margin:1.25rem 0;text-align:center;font-family:'Courier New',monospace;font-size:1.05rem;font-weight:600;color:var(--primary-dark)}

        /* SIM SECTIONS */
        .sim-section{background:linear-gradient(135deg,#f0f9ff,#e0f2fe);border-radius:16px;padding:1.75rem;margin:1.5rem 0;border:1px solid rgba(6,182,212,.3)}
        .sim-section h4{color:var(--cyan);margin-top:0}
        .sim-canvas-wrap{background:#fff;border-radius:12px;border:2px solid var(--border);padding:1rem;margin:1rem 0;text-align:center;overflow-x:auto}
        .sim-canvas-wrap canvas{max-width:100%;height:auto;display:block;margin:0 auto}

        /* CONTROLS */
        .controls{background:var(--bg);border-radius:12px;padding:1.25rem;margin:1rem 0;border:1px solid var(--border)}
        .ctrl-group{margin-bottom:.75rem}
        .ctrl-group:last-child{margin-bottom:0}
        .ctrl-label{display:block;font-weight:500;font-size:.9rem;color:var(--text);margin-bottom:.35rem}
        .slider-row{display:flex;align-items:center;gap:1rem}
        .slider-row input[type="range"]{flex:1;height:6px;-webkit-appearance:none;appearance:none;background:var(--bg3);border-radius:6px;outline:none}
        .slider-row input[type="range"]::-webkit-slider-thumb{-webkit-appearance:none;width:18px;height:18px;background:linear-gradient(135deg,var(--primary),var(--primary-light));border-radius:50%;cursor:pointer;box-shadow:0 2px 6px rgba(37,99,235,.3)}
        .slider-row input[type="range"]::-moz-range-thumb{width:18px;height:18px;background:linear-gradient(135deg,var(--primary),var(--primary-light));border-radius:50%;cursor:pointer;border:none}
        .val-badge{background:var(--primary);color:#fff;padding:.2rem .6rem;border-radius:8px;font-weight:600;font-size:.85rem;min-width:55px;text-align:center;white-space:nowrap}
        .status-badge{display:inline-block;padding:.25rem .75rem;border-radius:8px;font-weight:600;font-size:.8rem;margin-top:.5rem}
        .status-badge.normal{background:#dcfce7;color:#166534}
        .status-badge.critical{background:#fef3c7;color:#92400e}
        .status-badge.tir{background:#fee2e2;color:#991b1b}
        .explanation{font-style:italic;color:var(--text-sec);font-size:.85rem;margin-top:.35rem}

        /* CALCULATORS */
        .calc-section{background:var(--bg);border-radius:16px;padding:1.75rem;margin:1.5rem 0;border:1px solid var(--border)}
        .calc-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:1.25rem;margin:1rem 0}
        .calc-item{background:#fff;padding:1.25rem;border-radius:12px;border:1px solid var(--border)}
        .calc-item label{display:block;font-weight:500;font-size:.9rem;margin-bottom:.25rem}
        input[type="number"],select{width:100%;padding:.65rem .85rem;border:2px solid var(--border);border-radius:10px;font-size:.95rem;transition:border-color .2s;background:#fff;margin-top:.25rem;margin-bottom:.75rem}
        input[type="number"]:focus,select:focus{outline:none;border-color:var(--primary);box-shadow:0 0 0 3px rgba(37,99,235,.1)}
        button{background:linear-gradient(135deg,var(--primary),var(--primary-light));color:#fff;border:none;padding:.75rem 1.25rem;border-radius:10px;font-size:.95rem;font-weight:600;cursor:pointer;transition:all .2s;box-shadow:0 2px 8px rgba(37,99,235,.25);margin:.25rem 0}
        button:hover{transform:translateY(-1px);box-shadow:0 4px 12px rgba(37,99,235,.35)}
        button:active{transform:translateY(0)}
        .result-box{background:linear-gradient(135deg,#f0fdf4,#dcfce7);border:2px solid var(--success);border-radius:10px;padding:1rem 1.25rem;margin-top:.75rem;font-weight:500;min-height:44px}
        .result-box.error{background:linear-gradient(135deg,#fef2f2,#fecaca);border-color:#f87171}

        /* PRACTICAL */
        .practical{background:linear-gradient(135deg,#fffbeb,#fef3c7);border-left:4px solid var(--warning);border-radius:12px;padding:1.25rem 1.5rem;margin:1.25rem 0}
        .practical-method{background:linear-gradient(135deg,#f0f9ff,#e0f2fe);border:2px solid var(--cyan);border-radius:16px;padding:1.75rem;margin:1.5rem 0}
        .practical-method h5{color:var(--cyan);font-size:1.05rem;font-weight:600;margin-bottom:.75rem;padding-bottom:.5rem;border-bottom:2px solid rgba(6,182,212,.2)}
        .practical-method ol,.practical-method ul{padding-left:1.5rem;margin-bottom:1rem}
        .practical-method li{margin-bottom:.5rem;line-height:1.6}

        /* EM SPECTRUM */
        .em-spectrum{margin:1.5rem 0}
        .spectrum-bar{display:flex;border-radius:10px;overflow:hidden;height:50px;box-shadow:var(--shadow)}
        .spectrum-seg{flex:1;display:flex;align-items:center;justify-content:center;font-size:.7rem;font-weight:600;color:#fff;text-shadow:0 1px 2px rgba(0,0,0,.4);min-width:0;padding:0 .25rem}
        .spectrum-labels{display:flex;justify-content:space-between;font-size:.8rem;color:var(--text-sec);margin-top:.5rem;padding:0 .25rem}

        /* QUIZ */
        .quiz-wrap{background:var(--bg);border-radius:16px;padding:1.75rem;border:2px solid var(--border)}
        .q-card{background:#fff;border-radius:12px;padding:1.25rem;margin-bottom:1.25rem;border:1px solid var(--border);transition:box-shadow .2s}
        .q-card:hover{box-shadow:var(--shadow)}
        .q-card p{font-weight:600;margin-bottom:.75rem}
        .q-card label{display:block;padding:.4rem .5rem;cursor:pointer;border-radius:6px;transition:background .2s;font-size:.95rem}
        .q-card label:hover{background:var(--bg2)}
        input[type="radio"]{margin-right:.6rem;accent-color:var(--primary);transform:scale(1.15)}

        /* FOOTER */
        .footer{text-align:center;padding:2rem 1rem;color:var(--text-sec);font-size:.85rem}

        /* RESPONSIVE */
        @media(max-width:768px){
            .container{padding:1rem}
            .card-body{padding:1.25rem}
            .nav{padding:.6rem 1rem;gap:.75rem}
            .nav-links{gap:.25rem}
            .nav-links a{font-size:.75rem;padding:.25rem .5rem}
            .slider-row{flex-direction:column;gap:.5rem}
            .val-badge{align-self:flex-start}
            .calc-grid{grid-template-columns:1fr}
            .spectrum-seg{font-size:.55rem}
        }