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

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            min-height: 100vh;
            overflow-x: hidden;
            position: relative;
        }

        .math-symbols {
            position: absolute;
            width: 100%;
            height: 100%;
            overflow: hidden;
            opacity: 0.1;
            pointer-events: none;
        }

        .symbol {
            position: absolute;
            font-size: 3rem;
            color: white;
            animation: float 20s infinite;
        }

        @keyframes float {
            0%, 100% {
                transform: translateY(0) rotate(0deg);
            }
            50% {
                transform: translateY(-30px) rotate(180deg);
            }
        }

        nav {
            background: rgba(255, 255, 255, 0.1);
            backdrop-filter: blur(10px);
            padding: 20px 0;
            position: sticky;
            top: 0;
            z-index: 100;
            border-bottom: 1px solid rgba(255, 255, 255, 0.2);
        }

        .nav-container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 20px;
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .logo-nav {
            display: flex;
            align-items: center;
            gap: 12px;
        }

        .logo-icon {
            width: 50px;
            height: 50px;
            background: white;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 1.8rem;
            color: #667eea;
            font-weight: bold;
        }

        .logo-text {
            color: white;
            font-size: 1.5rem;
            font-weight: bold;
        }

        .btn-login-nav {
            background: white;
            color: #667eea;
            padding: 10px 25px;
            border-radius: 25px;
            font-weight: 600;
            transition: transform 0.2s, box-shadow 0.2s;
            text-decoration: none;
        }

        .btn-login-nav:hover {
            transform: translateY(-2px);
            box-shadow: 0 5px 15px rgba(255, 255, 255, 0.3);
        }

        .hero {
            max-width: 800px;
            margin: 60px auto;
            padding: 0 20px;
            text-align: center;
            position: relative;
            z-index: 10;
        }

        .hero h1 {
            color: white;
            font-size: 3.5rem;
            margin-bottom: 20px;
            animation: slideDown 0.8s ease-out;
        }

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

        .hero p {
            color: rgba(255, 255, 255, 0.9);
            font-size: 1.2rem;
            margin-bottom: 40px;
            animation: slideDown 0.8s ease-out 0.2s both;
        }

        .hero-image img {
         max-width: 100%;
    height: auto;
    border-radius: 20px;
        }

        .btn-start {
            padding: 18px 50px;
            border-radius: 30px;
            font-size: 1.2rem;
            font-weight: 600;
            cursor: pointer;
            transition: transform 0.2s, box-shadow 0.2s;
            text-decoration: none;
            display: inline-block;
            background: white;
            color: #667eea;
            border: none;
            animation: slideDown 0.8s ease-out 0.6s both;
        }

        .btn-start:hover {
            transform: translateY(-3px);
            box-shadow: 0 10px 25px rgba(255, 255, 255, 0.3);
        }

        .notebook-container {
            max-width: 800px;
            margin: 100px auto 80px;
            padding: 0 20px;
            position: relative;
            z-index: 10;
        }

        .notebook {
            position: relative;
            perspective: 1500px;
            height: 450px;
        }

        .page {
            position: absolute;
            width: 100%;
            height: 100%;
            background: white;
            border-radius: 10px;
            box-shadow: 0 10px 40px rgba(0, 0, 0, 0.3);
            padding: 50px 40px;
            transform-origin: left center;
            transition: transform 0.8s ease;
            border-left: 30px solid #f0f0f0;
        }

        .page::before {
            content: '';
            position: absolute;
            left: 15px;
            top: 0;
            width: 2px;
            height: 100%;
            background: repeating-linear-gradient(
                to bottom,
                #e74c3c 0px,
                #e74c3c 2px,
                transparent 2px,
                transparent 30px
            );
        }

        .page-1 {
            z-index: 3;
            transform: rotateY(0deg);
        }

        .page-2 {
            z-index: 2;
            transform: rotateY(0deg);
        }

        .page-3 {
            z-index: 1;
            transform: rotateY(0deg);
        }

        .page-1.flipped {
            transform: rotateY(-180deg);
            z-index: 0;
        }

        .page-2.flipped {
            transform: rotateY(-180deg);
            z-index: 0;
        }

        .page-content {
            text-align: center;
        }

        .page-icon {
            width: 80px;
            height: 80px;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            margin: 0 auto 25px;
            font-size: 2.5rem;
            color: white;
        }

        .page h3 {
            color: #333;
            font-size: 1.8rem;
            margin-bottom: 20px;
        }

        .page p {
            color: #666;
            line-height: 1.8;
            font-size: 1.1rem;
        }

        .page-indicator {
            text-align: center;
            margin-top: 30px;
            display: flex;
            gap: 10px;
            justify-content: center;
        }

        .dot {
            width: 12px;
            height: 12px;
            border-radius: 50%;
            background: rgba(255, 255, 255, 0.5);
            cursor: pointer;
            transition: all 0.3s;
        }

        .dot.active {
            background: white;
            width: 30px;
            border-radius: 6px;
        }

        @media (max-width: 768px) {
            .hero h1 {
                font-size: 2.5rem;
            }

            .hero-image {
                height: 250px;
                font-size: 3.5rem;
            }

            .notebook {
                height: 500px;
            }

            .page {
                padding: 40px 30px;
            }
        }