.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 for theming */
        :root {
            --bg-gradient-start: #667eea;
            --bg-gradient-end: #764ba2;
            --primary-color: #4f46e5;
            --primary-light: #818cf8;
            --primary-dark: #3730a3;
            --card-bg: #ffffff;
            --text-primary: #1f2937;
            --text-secondary: #6b7280;
            --border-color: #e5e7eb;
            --shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
            --shadow-hover: 0 20px 40px rgba(0, 0, 0, 0.15);
            --success-color: #10b981;
            --warning-color: #f59e0b;
            --danger-color: #ef4444;
            --info-color: #3b82f6;
        }

        body.dark-mode {
            --bg-gradient-start: #1e1b4b;
            --bg-gradient-end: #0f172a;
            --card-bg: #1e293b;
            --text-primary: #f1f5f9;
            --text-secondary: #cbd5e1;
            --border-color: #334155;
            --shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
            --shadow-hover: 0 20px 40px rgba(0, 0, 0, 0.7);
        }

        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Inter', sans-serif;
            background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
            min-height: 100vh;
            color: var(--text-primary);
            line-height: 1.6;
            overflow-x: hidden;
        }

        /* Floating background decorations */
        .bg-decoration {
            position: fixed;
            border-radius: 50%;
            background: rgba(255, 255, 255, 0.1);
            pointer-events: none;
            z-index: 0;
        }

        .bg-decoration:nth-child(1) {
            width: 300px;
            height: 300px;
            top: -100px;
            right: -100px;
        }

        .bg-decoration:nth-child(2) {
            width: 200px;
            height: 200px;
            bottom: 100px;
            left: -50px;
        }

        /* Navigation */
        nav {
            position: sticky;
            top: 0;
            background: rgba(255, 255, 255, 0.95);
            backdrop-filter: blur(10px);
            padding: 1rem 2rem;
            box-shadow: var(--shadow);
            z-index: 1000;
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
        }

        body.dark-mode nav {
            background: rgba(30, 41, 59, 0.95);
        }

        nav h1 {
            font-size: 1.5rem;
            color: var(--primary-color);
            flex: 1 1 auto;
        }

        nav ul {
            list-style: none;
            display: flex;
            gap: 1.5rem;
            flex-wrap: wrap;
            align-items: center;
        }

        nav a {
            text-decoration: none;
            color: var(--text-primary);
            font-weight: 500;
            transition: color 0.3s;
            font-size: 0.95rem;
        }

        nav a:hover {
            color: var(--primary-color);
        }

        #darkModeToggle {
            background: var(--primary-color);
            color: white;
            border: none;
            padding: 0.5rem 1rem;
            border-radius: 20px;
            cursor: pointer;
            font-size: 0.9rem;
            transition: background 0.3s;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        #darkModeToggle:hover {
            background: var(--primary-dark);
        }

        /* Container */
        .container {
            max-width: 1200px;
            margin: 2rem auto;
            padding: 0 2rem;
            position: relative;
            z-index: 1;
        }

        /* Section styling */
        section {
            background: var(--card-bg);
            border-radius: 16px;
            padding: 2.5rem;
            margin-bottom: 2rem;
            box-shadow: var(--shadow);
            transition: transform 0.3s, box-shadow 0.3s;
            animation: slideIn 0.6s ease-out;
        }

        section:hover {
            transform: translateY(-5px);
            box-shadow: var(--shadow-hover);
        }

        @keyframes slideIn {
            from {
                opacity: 0;
                transform: translateY(30px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        h2 {
            color: var(--primary-color);
            margin-bottom: 1.5rem;
            font-size: 2rem;
            border-bottom: 3px solid var(--primary-color);
            padding-bottom: 0.5rem;
        }

        h3 {
            color: var(--primary-dark);
            margin-top: 2rem;
            margin-bottom: 1rem;
            font-size: 1.5rem;
        }

        h4 {
            color: var(--text-primary);
            margin-top: 1.5rem;
            margin-bottom: 0.75rem;
            font-size: 1.2rem;
        }

        p {
            margin-bottom: 1rem;
            color: var(--text-secondary);
        }

        ul, ol {
            margin-left: 2rem;
            margin-bottom: 1rem;
            color: var(--text-secondary);
        }

        li {
            margin-bottom: 0.5rem;
        }

        /* Formula boxes */
        .formula-box {
            background: linear-gradient(135deg, #eff6ff 0%, #dbeafe 100%);
            border-left: 4px solid var(--primary-color);
            padding: 1.5rem;
            margin: 1.5rem 0;
            border-radius: 8px;
            font-family: 'Courier New', monospace;
            font-size: 1.2rem;
            font-weight: bold;
            color: var(--primary-dark);
        }

        body.dark-mode .formula-box {
            background: linear-gradient(135deg, #1e3a8a 0%, #1e40af 100%);
            color: #dbeafe;
        }

        /* Special content boxes */
        .practical-box {
            background: linear-gradient(135deg, #ecfdf5 0%, #d1fae5 100%);
            border-left: 4px solid var(--success-color);
            padding: 1.5rem;
            margin: 1.5rem 0;
            border-radius: 8px;
        }

        body.dark-mode .practical-box {
            background: linear-gradient(135deg, #064e3b 0%, #065f46 100%);
        }

        .example-box {
            background: linear-gradient(135deg, #fffbeb 0%, #fef3c7 100%);
            border-left: 4px solid var(--warning-color);
            padding: 1.5rem;
            margin: 1.5rem 0;
            border-radius: 8px;
        }

        body.dark-mode .example-box {
            background: linear-gradient(135deg, #78350f 0%, #92400e 100%);
        }

        .warning-box {
            background: linear-gradient(135deg, #fef2f2 0%, #fee2e2 100%);
            border-left: 4px solid var(--danger-color);
            padding: 1.5rem;
            margin: 1.5rem 0;
            border-radius: 8px;
        }

        body.dark-mode .warning-box {
            background: linear-gradient(135deg, #7f1d1d 0%, #991b1b 100%);
        }

        /* Calculator and simulation containers */
        .calculator, .simulation {
            background: #f8fafc;
            border: 2px solid var(--border-color);
            border-radius: 12px;
            padding: 1.5rem;
            margin: 1.5rem 0;
        }

        body.dark-mode .calculator,
        body.dark-mode .simulation {
            background: #0f172a;
        }

        .input-group {
            margin-bottom: 1rem;
        }

        label {
            display: block;
            margin-bottom: 0.5rem;
            font-weight: 500;
            color: var(--text-primary);
        }

        input[type="number"],
        input[type="range"],
        select {
            width: 100%;
            padding: 0.75rem;
            border: 2px solid var(--border-color);
            border-radius: 8px;
            font-size: 1rem;
            background: var(--card-bg);
            color: var(--text-primary);
            transition: border-color 0.3s;
        }

        input[type="number"]:focus,
        select:focus {
            outline: none;
            border-color: var(--primary-color);
        }

        input[type="range"] {
            padding: 0;
        }

        button {
            background: var(--primary-color);
            color: white;
            border: none;
            padding: 0.75rem 1.5rem;
            border-radius: 8px;
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: background 0.3s, transform 0.2s;
            margin: 0.5rem 0.5rem 0.5rem 0;
        }

        button:hover {
            background: var(--primary-dark);
            transform: translateY(-2px);
        }

        button:active {
            transform: translateY(0);
        }

        .result {
            background: #eff6ff;
            border-left: 4px solid var(--info-color);
            padding: 1rem;
            margin-top: 1rem;
            border-radius: 8px;
            color: var(--text-primary);
        }

        body.dark-mode .result {
            background: #1e3a8a;
        }

        .slider-container {
            margin: 1rem 0;
        }

        .slider-value {
            display: inline-block;
            background: var(--primary-color);
            color: white;
            padding: 0.25rem 0.75rem;
            border-radius: 12px;
            font-size: 0.9rem;
            margin-left: 0.5rem;
        }

        /* Canvas and SVG containers */
        canvas {
            border: 2px solid var(--border-color);
            border-radius: 8px;
            max-width: 100%;
            display: block;
            margin: 1rem auto;
            background: white;
        }

        body.dark-mode canvas {
            background: #1e293b;
        }

        svg {
            max-width: 100%;
            height: auto;
            display: block;
            margin: 1rem auto;
        }

        /* Quiz styling */
        .quiz-question {
            background: #f8fafc;
            border: 2px solid var(--border-color);
            border-radius: 12px;
            padding: 1.5rem;
            margin: 1rem 0;
        }

        body.dark-mode .quiz-question {
            background: #0f172a;
        }

        .quiz-options {
            list-style: none;
            margin: 1rem 0;
        }

        .quiz-options li {
            margin: 0.5rem 0;
        }

        .quiz-options input[type="radio"] {
            margin-right: 0.5rem;
        }

        .quiz-options label {
            cursor: pointer;
            display: inline;
            font-weight: normal;
        }

        .quiz-feedback {
            margin-top: 1rem;
            padding: 1rem;
            border-radius: 8px;
            display: none;
        }

        .quiz-feedback.correct {
            background: #d1fae5;
            border-left: 4px solid var(--success-color);
            color: #065f46;
            display: block;
        }

        .quiz-feedback.incorrect {
            background: #fee2e2;
            border-left: 4px solid var(--danger-color);
            color: #991b1b;
            display: block;
        }

        body.dark-mode .quiz-feedback.correct {
            background: #065f46;
            color: #d1fae5;
        }

        body.dark-mode .quiz-feedback.incorrect {
            background: #991b1b;
            color: #fee2e2;
        }

        .progress-bar {
            width: 100%;
            height: 30px;
            background: var(--border-color);
            border-radius: 15px;
            overflow: hidden;
            margin: 1rem 0;
        }

        .progress-fill {
            height: 100%;
            background: linear-gradient(90deg, var(--success-color) 0%, var(--primary-color) 100%);
            transition: width 0.3s ease;
            display: flex;
            align-items: center;
            justify-content: center;
            color: white;
            font-weight: bold;
        }

        /* Grid layout for responsive design */
        .grid-2 {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 1.5rem;
            margin: 1.5rem 0;
        }

        /* Responsive design */
        @media (max-width: 768px) {
            nav {
                flex-direction: column;
                align-items: flex-start;
            }

            nav ul {
                width: 100%;
                justify-content: flex-start;
                margin-top: 1rem;
            }

            .container {
                padding: 0 1rem;
            }

            section {
                padding: 1.5rem;
            }

            h2 {
                font-size: 1.5rem;
            }

            h3 {
                font-size: 1.25rem;
            }
        }

        /* Smooth scroll */
        html {
            scroll-behavior: smooth;
        }

        /* Learning outcomes badge */
        .learning-outcome {
            display: inline-block;
            background: var(--primary-light);
            color: white;
            padding: 0.25rem 0.75rem;
            border-radius: 12px;
            font-size: 0.85rem;
            margin: 0.25rem;
            font-weight: 500;
        }

        /* Animation for circuit elements */
        @keyframes flow {
            0% {
                offset-distance: 0%;
            }
            100% {
                offset-distance: 100%;
            }
        }

        .electron {
            animation: flow 3s linear infinite;
        }

        /* Preset buttons */
        .preset-buttons {
            display: flex;
            flex-wrap: wrap;
            gap: 0.5rem;
            margin: 1rem 0;
        }

        .preset-btn {
            background: var(--info-color);
            padding: 0.5rem 1rem;
            font-size: 0.9rem;
        }

        .preset-btn:hover {
            background: #2563eb;
        }