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

        body {
            font-family: 'Inter', 'Poppins', sans-serif;
            color: #2c3e50;
            background: #f5f6fa;
            line-height: 1.6;
            overflow-x: hidden;
        }

        .progress-container {
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 5px;
            background: #ecf0f1;
            z-index: 2000;
        }

        .progress-bar {
            height: 100%;
            background: #3498db;
            width: 0;
            transition: width 0.3s ease;
        }

        .progress-text {
            position: fixed;
            top: 10px;
            left: 50%;
            transform: translate(-50%, -20px);
            background: rgba(52, 152, 219, 0.7);
            color: white;
            padding: 0.5rem 1rem;
            border-radius: 20px;
            font-size: 0.8rem;
            font-weight: 600;
            z-index: 2001;
            opacity: 0;
            max-width: 300px;
            text-align: center;
            box-shadow: 0 2px 8px rgba(0, 0, 0, 0.3);
            transition: opacity 0.3s ease, transform 0.3s ease, scale 0.3s ease;
        }

        .progress-text.show {
            opacity: 1;
            transform: translate(-50%, 0);
            scale: 1;
        }

        .progress-text.hide {
            opacity: 0;
            transform: translate(-50%, -20px) scale(0.95);
        }

        header {
            background: linear-gradient(90deg, #2c3e50 0%, #3498db 100%);
            color: white;
            padding: 1.5rem 0;
            position: fixed;
            width: 100%;
            top: 5px;
            z-index: 1000;
            box-shadow: 0 4px 12px rgba(0,0,0,0.15);
        }

        nav {
            max-width: 1400px;
            margin: 0 auto;
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 0 2rem;
        }

        .logo {
            display: flex;
            flex-direction: column;
            align-items: flex-start;
        }

        .logo-main {
            font-size: 1.9rem;
            font-weight: 700;
            letter-spacing: 1px;
            position: relative;
        }

        .logo-main::after {
            content: '∑';
            position: absolute;
            font-size: 1rem;
            top: 0;
            right: -20px;
            color: #ecf0f1;
        }

        .logo-sub {
            font-size: 0.9rem;
            font-weight: 400;
            color: #ecf0f1;
            text-transform: uppercase;
        }

        .nav-links {
            list-style: none;
            display: flex;
            gap: 1.5rem;
        }

        .nav-links a {
            color: white;
            text-decoration: none;
            font-weight: 400;
            transition: color 0.3s ease;
            position: relative;
        }

        .nav-links a:hover::after {
            content: '→';
            position: absolute;
            right: -15px;
            font-size: 0.8rem;
        }

        .hero {
            margin-top: 65px;
            padding: 3rem 2rem;
            text-align: center;
            background: rgba(255, 255, 255, 0.2);
            backdrop-filter: blur(10px);
            border: 1px solid rgba(255, 255, 255, 0.3);
            box-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
            position: relative;
            overflow: hidden;
            max-width: 1400px;
            margin-left: auto;
            margin-right: auto;
            border-radius: 10px;
        }

        .hero::before {
            content: 'f(x) = x²';
            position: absolute;
            top: 20px;
            left: 20px;
            font-size: 2rem;
            color: #3498db;
            opacity: 0.1;
            transform: rotate(-30deg);
        }

        .hero h1 {
            font-size: 2.5rem;
            text-align: center;
            margin-bottom: 2rem;
            color: #3498db;
            font-weight: 700;
        }

        .video-container {
            max-width: 900px;
            margin: 0 auto;
            border-radius: 10px;
            overflow: hidden;
            box-shadow: 0 8px 24px rgba(0,0,0,0.2);
            position: relative;
            z-index: 1;
        }

        .video-container iframe {
            width: 100%;
            height: 500px;
            border: none;
        }

        .quiz-containers {
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 2rem;
            margin: 2rem auto;
            max-width: 1200px;
            justify-content: center;
        }

        .quiz-container {
            background: linear-gradient(135deg, rgba(255, 255, 255, 0.1), rgba(52, 152, 219, 0.05));
            backdrop-filter: blur(12px);
            border: 1px solid rgba(52, 152, 219, 0.2);
            box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1), inset 0 2px 4px rgba(255, 255, 255, 0.2);
            padding: 2.5rem;
            border-radius: 15px;
            text-align: center;
            position: relative;
            z-index: 1;
            max-width: 1200px;
            width: 100%;
            transition: transform 0.3s ease, box-shadow 0.3s ease;
        }

        .quiz-container:hover {
            transform: translateY(-5px);
            box-shadow: 0 12px 40px rgba(0, 0, 0, 0.15), inset 0 2px 6px rgba(255, 255, 255, 0.3);
        }

        .quiz-container h3 {
            font-size: 1.6rem;
            color: #3498db;
            margin-bottom: 1rem;
            font-weight: 700;
            text-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
        }

        .quiz-status {
            margin-bottom: 1rem;
        }

        .quiz-progress-container {
            background: rgba(255, 255, 255, 0.15);
            border: 1px solid rgba(52, 152, 219, 0.2);
            border-radius: 10px;
            height: 1.2rem;
            overflow: hidden;
            transition: border 0.3s ease;
        }

        .quiz-progress-container:hover {
            border: 1px solid #3498db;
        }

        .quiz-progress-bar {
            height: 100%;
            background: linear-gradient(135deg, rgba(255, 255, 255, 0.1), rgba(52, 152, 219, 0.15));
            width: 0;
            transition: width 0.3s ease;
        }

        .quiz-question {
            font-size: 1.2rem;
            margin-bottom: 1.5rem;
            font-weight: 500;
            color: #2c3e50;
            text-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
        }

        .quiz-image {
            max-width: 100%;
            margin-bottom: 1rem;
            display: none;
        }

        .quiz-image img {
            max-width: 100%;
            height: auto;
            border-radius: 8px;
            border: 1px solid rgba(52, 152, 219, 0.2);
            box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
        }

        .quiz-options {
            display: flex;
            flex-direction: column;
            gap: 1rem;
        }

        .quiz-option {
            background: rgba(255, 255, 255, 0.15);
            padding: 0.9rem;
            border-radius: 10px;
            cursor: pointer;
            transition: background 0.3s ease, transform 0.3s ease, border 0.3s ease;
            border: 1px solid rgba(52, 152, 219, 0.2);
            font-size: 1.2rem;
            font-weight: 500;
            color: #2c3e50;
            text-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
        }

        .quiz-option:hover {
            background: rgba(52, 152, 219, 0.15);
            border: 1px solid #3498db;
            transform: translateY(-3px);
        }

        .quiz-option.incorrect-answer {
            animation: shake 0.4s ease-in-out;
            border: 2px solid #e74c3c;
        }

        .time-remaining {
            background: rgba(255, 255, 255, 0.15);
            padding: 0.9rem;
            border-radius: 10px;
            border: 1px solid rgba(52, 152, 219, 0.2);
            font-size: 1.2rem;
            font-weight: 500;
            color: #2c3e50;
            text-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
            margin-top: 1rem;
            transition: background 0.3s ease, transform 0.3s ease, border 0.3s ease;
        }

        .time-remaining:hover {
            background: rgba(52, 152, 219, 0.15);
            border: 1px solid #3498db;
            transform: translateY(-3px);
        }

        .next-btn {
            background: rgba(255, 255, 255, 0.15);
            padding: 0.9rem;
            border-radius: 10px;
            border: 1px solid rgba(52, 152, 219, 0.2);
            font-size: 1.2rem;
            font-weight: 500;
            color: #2c3e50;
            text-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
            margin-top: 1rem;
            cursor: pointer;
            transition: background 0.3s ease, transform 0.3s ease, border 0.3s ease;
        }

        .next-btn:hover {
            background: rgba(52, 152, 219, 0.15);
            border: 1px solid #3498db;
            transform: translateY(-3px);
        }

        .quiz-feedback {
            margin-top: 1rem;
            font-size: 1rem;
            line-height: 1.6;
            padding: 1rem;
            background: rgba(52, 152, 219, 0.08);
            border-radius: 10px;
            opacity: 0;
            transition: opacity 0.3s ease;
            font-weight: 400;
            max-width: 100%;
            word-wrap: break-word;
            overflow-wrap: break-word;
            box-sizing: border-box;
            color: #2c3e50;
            text-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
        }

        .quiz-feedback.show {
            opacity: 1;
        }

        .quiz-feedback.correct::before {
            content: '🎉 ';
        }

        .quiz-feedback.incorrect::before {
            content: '🤯 ';
            display: inline-block;
            animation: spin 0.5s ease-in-out;
        }

        .katex {
            font-size: 1.3em;
            color: #2c3e50;
            text-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
        }

        .section {
            padding: 3rem 2rem;
            max-width: 1400px;
            margin: 0 auto;
        }

        .section h2 {
            font-size: 2.5rem;
            text-align: center;
            margin-bottom: 2rem;
            color: #3498db;
            font-weight: 700;
        }

        .about-course {
            background: rgba(255, 255, 255, 0.2);
            backdrop-filter: blur(10px);
            border: 1px solid rgba(255, 255, 255, 0.3);
            box-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
            padding: 3rem;
            border-radius: 10px;
            position: relative;
        }

        .course-content {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
            gap: 2rem;
            margin-top: 2rem;
        }

        .course-item {
            background: #f9fbfd;
            padding: 1.5rem;
            border-radius: 8px;
            text-align: center;
            transition: background 0.3s ease;
            position: relative;
            overflow: hidden;
        }

        .course-item::before {
            content: '';
            position: absolute;
            top: 10px;
            right: 10px;
            font-size: 2rem;
            color: #3498db;
            opacity: 0.1;
        }

        .course-item:nth-child(1)::before { content: '∈'; }
        .course-item:nth-child(2)::before { content: 'aⁿ'; }
        .course-item:nth-child(3)::before { content: 'x²'; }
        .course-item:nth-child(4)::before { content: '[A]'; }
        .course-item:nth-child(5)::before { content: '≅'; }
        .course-item:nth-child(6)::before { content: 't(n)'; }
        .course-item:nth-child(7)::before { content: '≈'; }
        .course-item:nth-child(8)::before { content: '∑'; }
        .course-item:nth-child(9)::before { content: '∞'; }

        .course-item:hover {
            background: #e6f0fa;
        }

        .course-item::after {
            content: attr(data-symbol);
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%) rotate(-10deg);
            font-size: 1.5rem;
            color: #3498db;
            opacity: 0;
            transition: opacity 0.3s ease, transform 0.3s ease;
            z-index: 2;
        }

        .instructor {
            display: flex;
            gap: 3rem;
            align-items: center;
            background: rgba(255, 255, 255, 0.2);
            backdrop-filter: blur(10px);
            border: 1px solid rgba(255, 255, 255, 0.3);
            box-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
            padding: 3rem;
            border-radius: 10px;
            position: relative;
        }

        .instructor::after {
            content: '∮';
            position: absolute;
            bottom: 20px;
            right: 20px;
            font-size: 2rem;
            color: #3498db;
            opacity: 0.1;
        }

        .instructor-img {
            width: 220px;
            height: 220px;
            border-radius: 50%;
            background: #e0e0e0;
            flex-shrink: 0;
            border: 4px solid #3498db;
        }

        .instructor-info h3 {
            font-size: 2rem;
            color: #2c3e50;
            margin-bottom: 0.5rem;
            font-weight: 600;
        }

        .instructor-info p {
            font-size: 1.1rem;
            font-weight: 400;
        }

        .tutor-btn {
            display: inline-block;
            background: #e67e22;
            color: white;
            padding: 0.8rem 2rem;
            text-decoration: none;
            border-radius: 50px;
            font-size: 1.2rem;
            font-weight: 700;
            margin-top: 1rem;
            position: relative;
            overflow: hidden;
            perspective: 1000px;
            transition: transform 0.5s ease;
        }

        .tutor-btn::after {
            content: 'You Will Fall in Love with Math';
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: #e67e22;
            color: white;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 50px;
            transform: rotateY(180deg);
            opacity: 0;
            transition: opacity 0.5s ease, transform 0.5s ease;
        }

        .tutor-btn:hover {
            transform: rotateY(180deg);
        }

        .tutor-btn:hover::after {
            opacity: 1;
        }

        .cta-section {
            padding: 3rem 2rem;
            max-width: 1400px;
            margin: 0 auto;
            display: flex;
            justify-content: center;
        }

        .cta {
            display: flex;
            gap: 3rem;
            align-items: center;
            background: rgba(255, 255, 255, 0.2);
            backdrop-filter: blur(10px);
            border: 1px solid rgba(255, 255, 255, 0.3);
            box-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
            padding: 3rem;
            border-radius: 10px;
            position: relative;
        }

        .cta::before {
            content: 'π';
            position: absolute;
            top: 20px;
            left: 20px;
            font-size: 3rem;
            color: #3498db;
            opacity: 0.2;
        }

        .cta-info {
            flex: 1;
        }

        .cta-info h2 {
            font-size: 2rem;
            margin-bottom: 0.5rem;
            color: #3498db;
            font-weight: 600;
        }

        .cta-info p {
            font-size: 1.1rem;
            font-weight: 400;
        }

        .countdown {
            font-size: 1.3rem;
            margin: 1rem 0;
            color: #e67e22;
            font-weight: 600;
            display: grid;
            place-items: center;
        }

        .buy-btn {
            display: inline-block;
            background: #00cc00;
            color: white;
            padding: 0.8rem 2rem;
            text-decoration: none;
            border-radius: 50px;
            font-size: 1.2rem;
            font-weight: 700;
            margin-top: 1rem;
            position: relative;
            overflow: hidden;
            perspective: 1000px;
            transition: transform 0.5s ease;
            display: grid;
            place-items: center;
        }

        .buy-btn::after {
            content: 'Great Choice 😊';
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: #00cc00;
            color: white;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 50px;
            transform: rotateY(180deg);
            opacity: 0;
            transition: opacity 0.3s ease, transform 0.5s ease;
            display: grid;
            place-items: center;
        }

        .buy-btn:hover {
            transform: rotateY(180deg);
        }

        .buy-btn:hover::after {
            opacity: 1;
        }

        footer {
            text-align: center;
            padding: 1rem;
            background: rgba(44, 62, 80, 0.9);
            color: white;
            font-size: 0.9rem;
            font-weight: 400;
        }

        .loading-overlay {
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: #2c3e50;
            display: flex;
            justify-content: center;
            align-items: center;
            z-index: 2000;
            opacity: 1;
            transition: opacity 0.5s ease;
        }

        .loading-overlay.hidden {
            opacity: 0;
            pointer-events: none;
        }

        .loader {
            width: 60px;
            height: 60px;
            border: 5px solid #3498db;
            border-top-color: transparent;
            border-radius: 50%;
            animation: spin 1s linear infinite, oscillate 2s ease-in-out infinite;
        }

        .floating-icon {
            position: absolute;
            font-size: 2rem;
            opacity: 0.2;
            z-index: -1;
            animation: float 6s ease-in-out infinite;
        }

        @keyframes float {
            0% { transform: translateY(0) rotate(0deg); }
            50% { transform: translateY(-20px) rotate(10deg); }
            100% { transform: translateY(0) rotate(0deg); }
        }

        @keyframes shake {
            0%, 100% { transform: translateX(0); }
            20%, 60% { transform: translateX(-10px); }
            40%, 80% { transform: translateX(10px); }
        }

        @keyframes spin {
            0% { transform: rotate(0deg); }
            100% { transform: rotate(360deg); }
        }

        @keyframes oscillate {
            0%, 100% { transform: scale(1); }
            50% { transform: scale(1.2); }
        }

        @media (max-width: 768px) {
            .hero {
                margin-top: 60px;
                padding: 1rem 2rem;
                margin-bottom: 0.5rem;
            }

            .hero h1 {
                font-size: 2.2rem;
            }

            .video-container iframe {
                height: 300px;
            }

            .section {
                padding: 1rem 2rem;
                margin-bottom: 0.5rem;
            }

            .instructor, .cta {
                flex-direction: column;
                text-align: center;
            }

            .nav-links {
                gap: 1rem;
            }

            .nav-links a {
                font-size: 0.9rem;
            }

            .progress-text {
                font-size: 0.7rem;
                padding: 0.3rem 0.8rem;
            }

            .quiz-containers {
                grid-template-columns: 1fr;
                justify-content: center;
                align-items: center;
            }

            .quiz-container {
                max-width: 100%;
                padding: 2rem;
                backdrop-filter: blur(8px);
            }

            .quiz-question {
                font-size: 1.1rem;
            }

            .quiz-image img {
                border-radius: 6px;
            }

            .quiz-option {
                font-size: 1rem;
                border-radius: 8px;
            }

            .time-remaining {
                font-size: 1rem;
                border-radius: 8px;
            }

            .next-btn {
                font-size: 1rem;
                border-radius: 8px;
            }

            .quiz-progress-container {
                height: 1rem;
                border-radius: 8px;
            }

            .quiz-feedback {
                font-size: 0.9rem;
                line-height: 1.5;
                padding: 0.8rem;
                border-radius: 8px;
            }

            .logo-main {
                font-size: 1.6rem;
            }

            .logo-sub {
                font-size: 0.7rem;
            }

            .section h2 {
                font-size: 2rem;
            }

            .instructor-info h3, .cta-info h2 {
                font-size: 1.8rem;
            }

            .instructor-info p, .cta-info p {
                font-size: 1rem;
            }

            .floating-icon {
                font-size: 1.5rem;
            }
        }