.shell-nav{position:fixed;top:0;left:0;right:0;z-index:2000;background:rgba(26,26,46,0.85);backdrop-filter:blur(24px);-webkit-backdrop-filter:blur(24px);border-bottom:1px solid rgba(255,255,255,0.06)}
.shell-nav.scrolled{background:rgba(15,15,26,0.96);box-shadow:0 4px 30px rgba(0,0,0,0.5)}
.nav-inner{max-width:1280px;margin:0 auto;display:flex;align-items:center;justify-content:space-between;padding:0 32px;height:64px}
.nav-brand{display:flex;align-items:center;gap:12px;text-decoration:none;font-weight:700;font-size:17px;color:#f0f0f0}
.nav-brand .brand-icon{width:34px;height:34px;background:linear-gradient(135deg,#7DB6B1,#5a9e98);border-radius:10px;display:flex;align-items:center;justify-content:center;font-size:15px;font-weight:900;color:#0f0f1a}
.nav-brand span{color:#7DB6B1}
.nav-links{display:flex;align-items:center;gap:4px}
.nav-link{padding:8px 16px;border-radius:8px;text-decoration:none;font-size:14px;font-weight:600;color:#9ca3af}
.nav-link:hover{color:#f0f0f0;background:rgba(255,255,255,0.04)}
.nav-cta{padding:8px 24px;border-radius:8px;background:linear-gradient(135deg,#7DB6B1,#5a9e98);color:#0f0f1a;text-decoration:none;font-size:14px;font-weight:700;display:inline-block}
.nav-cta:hover{transform:translateY(-1px);box-shadow:0 4px 20px rgba(125,182,177,0.25)}
.nav-progress{position:absolute;bottom:-2px;left:0;height:2px;background:linear-gradient(90deg,#7DB6B1,#a3d4cf);width:0%;transition:width 0.1s linear}
.breadcrumbs{display:flex;align-items:center;gap:8px;padding:80px 32px 8px;max-width:1280px;margin:0 auto;font-size:13px;color:#6b7280}
.breadcrumbs a{color:#9ca3af;text-decoration:none}
.breadcrumbs a:hover{color:#7DB6B1}
.breadcrumbs .current{color:#f0f0f0;font-weight:600}
.breadcrumbs .separator{margin:0 2px}
.shell-nav{position:fixed;top:0;left:0;right:0;z-index:2000;background:rgba(26,26,46,0.85);backdrop-filter:blur(24px);-webkit-backdrop-filter:blur(24px);border-bottom:1px solid rgba(255,255,255,0.06)}.shell-nav.scrolled{background:rgba(15,15,26,0.96);box-shadow:0 4px 30px rgba(0,0,0,0.5)}.nav-inner{max-width:1280px;margin:0 auto;display:flex;align-items:center;justify-content:space-between;padding:0 32px;height:64px}.nav-brand{display:flex;align-items:center;gap:12px;text-decoration:none;font-weight:700;font-size:17px;color:#f0f0f0}.nav-brand .brand-icon{width:34px;height:34px;background:linear-gradient(135deg,#7DB6B1,#5a9e98);border-radius:10px;display:flex;align-items:center;justify-content:center;font-size:15px;font-weight:900;color:#0f0f1a}.nav-brand span{color:#7DB6B1}.nav-links{display:flex;align-items:center;gap:4px}.nav-link{padding:8px 16px;border-radius:8px;text-decoration:none;font-size:14px;font-weight:600;color:#9ca3af}.nav-link:hover{color:#f0f0f0;background:rgba(255,255,255,0.04)}.nav-cta{padding:8px 24px;border-radius:8px;background:linear-gradient(135deg,#7DB6B1,#5a9e98);color:#0f0f1a;text-decoration:none;font-size:14px;font-weight:700;display:inline-block}.nav-cta:hover{transform:translateY(-1px);box-shadow:0 4px 20px rgba(125,182,177,0.25)}.nav-progress{position:absolute;bottom:-2px;left:0;height:2px;background:linear-gradient(90deg,#7DB6B1,#a3d4cf);width:0%;transition:width 0.1s linear}.breadcrumbs{display:flex;align-items:center;gap:8px;padding:80px 32px 8px;max-width:1280px;margin:0 auto;font-size:13px;color:#6b7280}.breadcrumbs a{color:#9ca3af;text-decoration:none}.breadcrumbs a:hover{color:#7DB6B1}.breadcrumbs .current{color:#f0f0f0;font-weight:600}.breadcrumbs .separator{margin:0 2px}
/* ===== CSS VARIABLES ===== */
        :root {
            --bg: #f0f4f8;
            --bg-card: #ffffff;
            --text: #1e293b;
            --text-secondary: #475569;
            --text-muted: #64748b;
            --primary: #3b82f6;
            --primary-light: #dbeafe;
            --primary-dark: #1d4ed8;
            --accent-purple: #8b5cf6;
            --accent-pink: #ec4899;
            --accent-orange: #f97316;
            --accent-green: #10b981;
            --accent-yellow: #eab308;
            --accent-red: #ef4444;
            --accent-cyan: #06b6d4;
            --border: #e2e8f0;
            --shadow: 0 1px 3px rgba(0,0,0,0.08), 0 1px 2px rgba(0,0,0,0.06);
            --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
            --shadow-lg: 0 10px 30px rgba(0,0,0,0.1);
            --radius: 12px;
            --radius-lg: 16px;
            --radius-xl: 20px;
            --font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
        }

        /* ===== RESET ===== */
        *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

        body {
            font-family: var(--font);
            background: var(--bg);
            color: var(--text);
            line-height: 1.7;
            overflow-x: hidden;
        }

        /* ===== NAVIGATION ===== */
        .top-nav {
            position: sticky;
            top: 0;
            z-index: 100;
            background: rgba(255,255,255,0.85);
            backdrop-filter: blur(12px);
            border-bottom: 1px solid var(--border);
            padding: 0 24px;
        }
        .top-nav-inner {
            max-width: 1200px;
            margin: 0 auto;
            display: flex;
            align-items: center;
            gap: 8px;
            height: 56px;
            overflow-x: auto;
            scrollbar-width: none;
        }
        .top-nav-inner::-webkit-scrollbar { display: none; }
        .nav-link {
            flex-shrink: 0;
            padding: 6px 14px;
            border-radius: 20px;
            font-size: 13px;
            font-weight: 500;
            color: var(--text-muted);
            text-decoration: none;
            transition: all 0.2s;
            white-space: nowrap;
        }
        .nav-link:hover, .nav-link.active {
            background: var(--primary-light);
            color: var(--primary-dark);
        }

        /* ===== LAYOUT ===== */
        .container {
            max-width: 960px;
            margin: 0 auto;
            padding: 24px 20px 80px;
        }

        /* ===== HERO ===== */
        .hero {
            background: linear-gradient(135deg, #1e40af 0%, #7c3aed 50%, #db2777 100%);
            border-radius: var(--radius-xl);
            padding: 60px 40px;
            text-align: center;
            color: #fff;
            margin-bottom: 40px;
            position: relative;
            overflow: hidden;
        }
        .hero::before {
            content: '';
            position: absolute;
            inset: 0;
            background: url("data:image/svg+xml,%3Csvg width='60' height='60' viewBox='0 0 60 60' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23ffffff' fill-opacity='0.05'%3E%3Cpath d='M36 34v-4h-2v4h-4v2h4v4h2v-4h4v-2h-4zm0-30V0h-2v4h-4v2h4v4h2V6h4V4h-4zM6 34v-4H4v4H0v2h4v4h2v-4h4v-2H6zM6 4V0H4v4H0v2h4v4h2V6h4V4H6z'/%3E%3C/g%3E%3C/g%3E%3C/svg%3E");
        }
        .hero h1 { font-size: 2.8rem; font-weight: 800; margin-bottom: 12px; position: relative; }
        .hero p { font-size: 1.15rem; opacity: 0.9; font-weight: 300; position: relative; }

        /* ===== SECTION CARDS ===== */
        .section-card {
            background: var(--bg-card);
            border: 1px solid var(--border);
            border-radius: var(--radius-lg);
            padding: 36px;
            margin-bottom: 32px;
            box-shadow: var(--shadow);
            transition: box-shadow 0.3s;
        }
        .section-card:hover { box-shadow: var(--shadow-md); }

        .section-header {
            display: flex;
            align-items: center;
            gap: 14px;
            margin-bottom: 24px;
        }
        .section-icon {
            width: 48px; height: 48px;
            border-radius: 12px;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 1.5rem;
            flex-shrink: 0;
        }
        .section-header h2 {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--text);
        }

        h3 {
            font-size: 1.15rem;
            font-weight: 600;
            color: var(--text);
            margin: 28px 0 12px;
        }
        h4 { font-size: 1rem; font-weight: 600; margin-bottom: 8px; }
        p { margin-bottom: 12px; color: var(--text-secondary); }
        strong { color: var(--text); }

        /* ===== LEARNING OUTCOMES ===== */
        .learning-outcome {
            background: linear-gradient(135deg, #ede9fe, #fce7f3);
            border-left: 4px solid var(--accent-purple);
            border-radius: 0 var(--radius) var(--radius) 0;
            padding: 16px 20px;
            margin-bottom: 20px;
        }
        .learning-outcome p {
            font-size: 0.9rem;
            color: var(--accent-purple);
            font-weight: 500;
            margin: 0;
        }

        /* ===== FORMULA BOXES ===== */
        .formula-box {
            background: linear-gradient(135deg, #fef3c7, #fde68a);
            border: 2px solid var(--accent-yellow);
            border-radius: var(--radius);
            padding: 20px 24px;
            margin: 20px 0;
            text-align: center;
        }
        .formula-box .main-formula {
            font-size: 1.3rem;
            font-weight: 700;
            color: var(--text);
            margin-bottom: 4px;
        }
        .formula-box .formula-detail {
            font-size: 0.9rem;
            color: var(--text-muted);
            margin: 0;
        }

        /* ===== EXAMPLE BOXES ===== */
        .example-box {
            background: #f0fdf4;
            border-left: 4px solid var(--accent-green);
            border-radius: 0 var(--radius) var(--radius) 0;
            padding: 16px 20px;
            margin: 16px 0;
        }
        .example-box p { color: #166534; margin: 0; }

        /* ===== EXPLANATION ===== */
        .explanation {
            background: #f0f9ff;
            border-left: 4px solid var(--accent-cyan);
            border-radius: 0 var(--radius) var(--radius) 0;
            padding: 14px 18px;
            margin: 12px 0;
            font-style: italic;
        }
        .explanation p { color: #0e7490; margin: 0; }

        /* ===== LISTS ===== */
        ul { list-style: none; padding: 0; margin-bottom: 16px; }
        li {
            padding: 6px 0 6px 28px;
            position: relative;
            color: var(--text-secondary);
        }
        li::before {
            content: '▸';
            position: absolute;
            left: 8px;
            color: var(--primary);
            font-weight: 700;
        }

        /* ===== INTERACTIVE PANELS ===== */
        .sim-panel {
            background: #f8fafc;
            border: 2px solid var(--border);
            border-radius: var(--radius-lg);
            padding: 24px;
            margin: 24px 0;
        }
        .sim-panel h3 {
            margin-top: 0;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        /* ===== FORM ELEMENTS ===== */
        label.input-label {
            display: block;
            font-size: 0.85rem;
            font-weight: 500;
            color: var(--text-muted);
            margin-bottom: 4px;
        }
        input[type="number"], select {
            width: 100%;
            padding: 10px 14px;
            border: 2px solid var(--border);
            border-radius: 8px;
            font-size: 0.95rem;
            font-family: var(--font);
            transition: border-color 0.2s;
            background: #fff;
        }
        input[type="number"]:focus, select:focus {
            outline: none;
            border-color: var(--primary);
            box-shadow: 0 0 0 3px rgba(59,130,246,0.15);
        }
        .input-row {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
            gap: 16px;
            margin-bottom: 16px;
        }

        /* ===== BUTTONS ===== */
        .btn {
            display: inline-flex;
            align-items: center;
            gap: 6px;
            padding: 10px 22px;
            border: none;
            border-radius: 8px;
            font-size: 0.9rem;
            font-weight: 600;
            font-family: var(--font);
            cursor: pointer;
            transition: all 0.2s;
        }
        .btn-primary {
            background: var(--primary);
            color: #fff;
        }
        .btn-primary:hover {
            background: var(--primary-dark);
            transform: translateY(-1px);
            box-shadow: 0 4px 12px rgba(59,130,246,0.3);
        }
        .btn-danger { background: var(--accent-red); color: #fff; }
        .btn-danger:hover { background: #dc2626; }
        .btn-success { background: var(--accent-green); color: #fff; }
        .btn-success:hover { background: #059669; }
        .btn-outline {
            background: transparent;
            border: 2px solid var(--border);
            color: var(--text-secondary);
        }
        .btn-outline:hover { border-color: var(--primary); color: var(--primary); }

        /* ===== RESULT DISPLAY ===== */
        .result-box {
            background: linear-gradient(135deg, #ecfdf5, #d1fae5);
            border: 2px solid var(--accent-green);
            border-radius: var(--radius);
            padding: 16px 20px;
            margin-top: 16px;
            font-weight: 600;
            color: #065f46;
            display: none;
        }
        .result-box.show { display: block; animation: slideIn 0.3s ease; }
        .result-box.error {
            background: linear-gradient(135deg, #fef2f2, #fecaca);
            border-color: var(--accent-red);
            color: #991b1b;
        }

        .working-steps {
            background: #fff;
            border: 1px solid var(--border);
            border-radius: 8px;
            padding: 16px;
            margin-top: 12px;
            font-family: 'Courier New', monospace;
            font-size: 0.85rem;
            white-space: pre-line;
            color: var(--text-secondary);
            display: none;
        }
        .working-steps.show { display: block; animation: slideIn 0.3s ease; }

        /* ===== CANVAS SIMULATIONS ===== */
        .sim-canvas-wrapper {
            background: #0f172a;
            border-radius: var(--radius);
            overflow: hidden;
            margin: 16px 0;
            position: relative;
        }
        .sim-canvas-wrapper canvas {
            display: block;
            width: 100%;
            height: auto;
        }
        .sim-controls {
            display: flex;
            flex-wrap: wrap;
            gap: 16px;
            align-items: end;
            margin: 16px 0;
        }
        .sim-control-group {
            display: flex;
            flex-direction: column;
            gap: 4px;
            min-width: 140px;
        }
        .sim-control-group label {
            font-size: 0.8rem;
            font-weight: 600;
            color: var(--text-muted);
        }
        .sim-control-group input[type="range"] {
            width: 100%;
            accent-color: var(--primary);
        }
        .sim-control-group .range-value {
            font-size: 0.8rem;
            color: var(--primary);
            font-weight: 600;
            text-align: center;
        }

        /* ===== INTERACTIVE PLUG ===== */
        .plug-diagram {
            display: flex;
            flex-wrap: wrap;
            gap: 24px;
            align-items: center;
            justify-content: center;
        }
        .plug-svg-container {
            flex-shrink: 0;
        }
        .plug-svg-container svg {
            cursor: pointer;
        }
        .plug-info-panel {
            flex: 1;
            min-width: 250px;
            background: #fff;
            border: 2px solid var(--border);
            border-radius: var(--radius);
            padding: 20px;
            min-height: 160px;
            transition: all 0.3s;
        }
        .plug-info-panel h4 { margin-bottom: 8px; }
        .plug-info-panel p { margin: 0; font-size: 0.9rem; }

        .wire-btn {
            padding: 8px 16px;
            border: 2px solid var(--border);
            border-radius: 8px;
            font-size: 0.85rem;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s;
            background: #fff;
            font-family: var(--font);
        }
        .wire-btn:hover { transform: translateY(-2px); box-shadow: var(--shadow-md); }
        .wire-btn.live { border-color: #92400e; color: #92400e; }
        .wire-btn.live.active { background: #92400e; color: #fff; }
        .wire-btn.neutral { border-color: #1e40af; color: #1e40af; }
        .wire-btn.neutral.active { background: #1e40af; color: #fff; }
        .wire-btn.earth { border-color: #15803d; color: #15803d; }
        .wire-btn.earth.active { background: #15803d; color: #fff; }

        /* ===== SAFETY SVG DIAGRAMS ===== */
        .safety-diagram {
            display: flex;
            justify-content: center;
            padding: 16px;
            margin: 12px 0;
        }
        .safety-diagram svg {
            max-width: 180px;
            height: auto;
        }

        /* ===== QUIZ ===== */
        .quiz-question-card {
            background: #fff;
            border: 1px solid var(--border);
            border-radius: var(--radius);
            padding: 20px;
            margin-bottom: 16px;
            transition: all 0.2s;
        }
        .quiz-question-card.correct { border-color: var(--accent-green); background: #f0fdf4; }
        .quiz-question-card.incorrect { border-color: var(--accent-red); background: #fef2f2; }

        .quiz-question-card p.q-text {
            font-weight: 600;
            color: var(--text);
            margin-bottom: 12px;
        }
        .quiz-option {
            display: flex;
            align-items: center;
            gap: 10px;
            padding: 8px 12px;
            border-radius: 8px;
            cursor: pointer;
            transition: background 0.15s;
            margin-bottom: 4px;
        }
        .quiz-option:hover { background: var(--primary-light); }
        .quiz-option input[type="radio"] {
            accent-color: var(--primary);
            transform: scale(1.15);
        }
        .quiz-option label {
            cursor: pointer;
            font-size: 0.9rem;
            color: var(--text-secondary);
        }
        .quiz-feedback {
            margin-top: 8px;
            padding: 8px 12px;
            border-radius: 8px;
            font-size: 0.85rem;
            font-weight: 500;
            display: none;
        }
        .quiz-feedback.show { display: block; animation: slideIn 0.3s ease; }
        .quiz-feedback.correct-fb { background: #dcfce7; color: #166534; }
        .quiz-feedback.incorrect-fb { background: #fee2e2; color: #991b1b; }

        .quiz-score-bar {
            background: var(--border);
            border-radius: 20px;
            height: 12px;
            margin: 16px 0;
            overflow: hidden;
        }
        .quiz-score-fill {
            height: 100%;
            border-radius: 20px;
            background: linear-gradient(90deg, var(--accent-green), #34d399);
            transition: width 0.6s ease;
            width: 0%;
        }

        /* ===== FUSE SELECTION ===== */
        .fuse-options {
            display: flex;
            gap: 12px;
            flex-wrap: wrap;
            margin: 16px 0;
        }
        .fuse-chip {
            padding: 10px 20px;
            border: 2px solid var(--border);
            border-radius: 20px;
            font-weight: 600;
            font-size: 0.9rem;
            cursor: default;
            transition: all 0.3s;
            background: #fff;
            font-family: var(--font);
        }
        .fuse-chip.recommended {
            border-color: var(--accent-green);
            background: #dcfce7;
            color: #166534;
            transform: scale(1.1);
            box-shadow: 0 4px 12px rgba(16,185,129,0.3);
        }
        .fuse-chip.too-low {
            border-color: var(--accent-red);
            background: #fee2e2;
            color: #991b1b;
        }
        .fuse-chip.too-high {
            border-color: var(--accent-orange);
            background: #fff7ed;
            color: #9a3412;
        }

        /* ===== ANIMATIONS ===== */
        @keyframes slideIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }
        @keyframes glow {
            0%, 100% { filter: drop-shadow(0 0 4px rgba(239,68,68,0.4)); }
            50% { filter: drop-shadow(0 0 12px rgba(239,68,68,0.8)); }
        }

        /* ===== SCROLL ANIMATIONS ===== */
        .fade-in {
            opacity: 0;
            transform: translateY(30px);
            transition: opacity 0.6s ease, transform 0.6s ease;
        }
        .fade-in.visible {
            opacity: 1;
            transform: translateY(0);
        }

        /* ===== RESPONSIVE ===== */
        @media (max-width: 640px) {
            .container { padding: 16px 12px 60px; }
            .hero { padding: 40px 20px; }
            .hero h1 { font-size: 2rem; }
            .section-card { padding: 24px 16px; }
            .sim-panel { padding: 16px; }
            .plug-diagram { flex-direction: column; }
            .input-row { grid-template-columns: 1fr; }
        }