* { margin: 0; padding: 0; box-sizing: border-box; }
        
        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            color: #fff;
            line-height: 1.6;
        }
        
        .container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }
        
        header {
            background: rgba(0,0,0,0.3);
            backdrop-filter: blur(10px);
            padding: 1.5rem 0;
            position: sticky;
            top: 0;
            z-index: 100;
        }
        
        nav { display: flex; justify-content: space-between; align-items: center; }
        .logo { 
            font-size: 1.8rem; 
            font-weight: bold;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }
        .logo svg {
            width: 1.8rem;
            height: 1.8rem;
            fill: currentColor;
        }
        
        .hero { text-align: center; padding: 4rem 0; }
        .hero h1 { font-size: 3rem; margin-bottom: 1rem; }
        .hero p { font-size: 1.2rem; opacity: 0.9; margin-bottom: 2rem; }
        
        .cta {
            display: inline-block;
            background: #fff;
            color: #667eea;
            padding: 1rem 2rem;
            border-radius: 50px;
            border: none;
            font-weight: bold;
            font-size: 1rem;
            cursor: pointer;
            transition: transform 0.3s;
        }
        .cta:hover { transform: translateY(-2px); }
        
        .topics {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 2rem;
            padding: 3rem 0;
        }
        
        .card {
            background: rgba(255,255,255,0.1);
            backdrop-filter: blur(10px);
            border-radius: 20px;
            padding: 2rem;
            cursor: pointer;
            transition: all 0.3s;
            border: 2px solid rgba(255,255,255,0.2);
        }
        
        .card:hover {
            transform: translateY(-5px);
            background: rgba(255,255,255,0.15);
        }
        
        .card.completed {
            border-color: #10b981;
            background: rgba(16, 185, 129, 0.2);
        }
        
        .icon { font-size: 2.5rem; margin-bottom: 1rem; }
        .card h3 { margin-bottom: 0.5rem; }
        
        .badge {
            display: inline-block;
            background: rgba(255,255,255,0.3);
            padding: 0.3rem 0.8rem;
            border-radius: 20px;
            font-size: 0.85rem;
            margin-top: 1rem;
        }
        
        .modal {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.8);
            z-index: 1000;
            overflow-y: auto;
        }
        
        .modal.active {
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 2rem;
        }
        
        .modal-content {
            background: #1a1a2e;
            border-radius: 20px;
            max-width: 800px;
            width: 100%;
            max-height: 90vh;
            overflow-y: auto;
            padding: 2rem;
            position: relative;
        }
        
        .close {
            position: absolute;
            top: 1rem;
            right: 1.5rem;
            font-size: 2rem;
            cursor: pointer;
            background: none;
            border: none;
            color: #fff;
        }
        
        .modal-content h2 { color: #667eea; margin-bottom: 1rem; }
        .modal-content h3 { color: #9f7aea; margin: 1.5rem 0 0.5rem; }
        .modal-content p { margin-bottom: 1rem; opacity: 0.9; }
        .modal-content ul { margin-left: 1.5rem; margin-bottom: 1rem; }
        .modal-content li { margin-bottom: 0.5rem; opacity: 0.9; }
        .modal-content strong { color: #fff; }
        
        .modal-content a {
            color: inherit;
            text-decoration: none;
            transition: opacity 0.3s;
        }
        
        .modal-content a:hover {
            opacity: 0.7;
        }
        
        .quiz-section {
            margin-top: 3rem;
            padding-top: 2rem;
            border-top: 2px solid rgba(255,255,255,0.2);
        }
        
        .quiz-question {
            background: rgba(255,255,255,0.05);
            padding: 1.5rem;
            border-radius: 15px;
            margin-bottom: 1.5rem;
        }
        
        .quiz-question h4 { color: #fff; margin-bottom: 1rem; }
        
        .quiz-options {
            display: flex;
            flex-direction: column;
            gap: 0.8rem;
        }
        
        .quiz-option {
            background: rgba(255,255,255,0.1);
            padding: 1rem;
            border-radius: 10px;
            cursor: pointer;
            transition: all 0.3s;
            border: 2px solid transparent;
        }
        
        .quiz-option:hover { background: rgba(255,255,255,0.15); }
        
        .quiz-option.selected {
            border-color: #667eea;
            background: rgba(102, 126, 234, 0.2);
        }
        
        .quiz-option.correct {
            border-color: #10b981;
            background: rgba(16, 185, 129, 0.2);
        }
        
        .quiz-option.incorrect {
            border-color: #ef4444;
            background: rgba(239, 68, 68, 0.2);
        }
        
        .quiz-feedback {
            margin-top: 1rem;
            padding: 1rem;
            border-radius: 10px;
            display: none;
        }
        
        .quiz-feedback.show { display: block; }
        
        .quiz-feedback.correct {
            background: rgba(16, 185, 129, 0.2);
            border: 2px solid #10b981;
        }
        
        .quiz-feedback.incorrect {
            background: rgba(239, 68, 68, 0.2);
            border: 2px solid #ef4444;
        }
        
        .submit-quiz {
            background: #667eea;
            color: #fff;
            border: none;
            padding: 1rem 2rem;
            border-radius: 50px;
            font-size: 1rem;
            font-weight: bold;
            cursor: pointer;
            margin-top: 1.5rem;
            transition: all 0.3s;
        }
        
        .submit-quiz:hover {
            background: #5568d3;
            transform: translateY(-2px);
        }
        
        .submit-quiz:disabled {
            opacity: 0.5;
            cursor: not-allowed;
        }
        
        .quiz-result {
            text-align: center;
            padding: 2rem;
            background: rgba(16, 185, 129, 0.2);
            border-radius: 15px;
            margin-top: 2rem;
            display: none;
        }
        
        .quiz-result.show { display: block; }
        .quiz-result h3 { color: #10b981; margin-bottom: 1rem; }
        
        .close-modal-bottom {
            background: rgba(255,255,255,0.1);
            color: #fff;
            border: 2px solid rgba(255,255,255,0.3);
            padding: 1rem 2rem;
            border-radius: 50px;
            font-size: 1rem;
            font-weight: bold;
            cursor: pointer;
            margin-top: 2rem;
            transition: all 0.3s;
            width: 100%;
        }
        
        .close-modal-bottom:hover {
            background: rgba(255,255,255,0.2);
            border-color: rgba(255,255,255,0.5);
        }
        
        footer {
            background: rgba(0,0,0,0.3);
            padding: 2rem 0;
            margin-top: 3rem;
            text-align: center;
        }
        
        footer .cta {
            margin-top: 1rem;
        }

        footer a {
            color: inherit;                 /*same color as the surrounding text*/
            text-decoration: none;
            transition: opacity 0.3s;       /* Smooth animation */
        }

        footer a:hover {
            opacity: 0.7;                   /* Lighter on hover */
        }
        
        .clickable-point {
            cursor: pointer;
            transition: all 0.3s;
            padding: 0.3rem;
            border-radius: 5px;
        }
        
        .clickable-point:hover {
            background: rgba(255,255,255,0.1);
        }
        
        .clickable-point.active {
            background: rgba(102, 126, 234, 0.3);
        }
        
        .explanation-box {
            margin-top: 2rem;
            padding: 1.5rem;
            background: rgba(102, 126, 234, 0.2);
            border-left: 4px solid #667eea;
            border-radius: 10px;
            display: none;
        }
        
        .explanation-box.show {
            display: block;
        }
        
        .explanation-box h4 {
            color: #667eea;
            margin-bottom: 0.5rem;
        }
        
        .welcome-modal-content {
            text-align: center;
        }
        
        .welcome-modal-content h2 {
            font-size: 2.5rem;
            margin-bottom: 1.5rem;
        }
        
        .welcome-modal-content .intro-text {
            font-size: 1.1rem;
            margin-bottom: 2rem;
            opacity: 0.9;
        }
        
        .learning-path {
            background: rgba(255,255,255,0.05);
            padding: 1.5rem;
            border-radius: 15px;
            margin: 2rem 0;
            text-align: left;
        }
        
        .learning-path h3 {
            color: #10b981;
            margin-bottom: 1rem;
        }
        
        .learning-path ul {
            list-style: none;
            margin-left: 0;
        }
        
        .learning-path li {
            padding: 0.5rem 0;
            padding-left: 0;
        }
        
        .learning-path li::before {
            content: "✓ ";
            color: #10b981;
            font-weight: bold;
            font-size: 1.2rem;
        }
        
        .learning-path li strong {
            white-space: nowrap;
        }
        
        .start-button {
            background: linear-gradient(135deg, #10b981, #059669);
            color: #fff;
            border: none;
            padding: 1.2rem 3rem;
            border-radius: 50px;
            font-size: 1.2rem;
            font-weight: bold;
            cursor: pointer;
            margin-top: 1.5rem;
            transition: all 0.3s;
            box-shadow: 0 4px 15px rgba(16, 185, 129, 0.4);
        }
        
        .start-button:hover {
            transform: translateY(-2px);
            box-shadow: 0 6px 20px rgba(16, 185, 129, 0.6);
        }
        
        @media (max-width: 768px) {
            .hero h1 { font-size: 2rem; }
            .topics { grid-template-columns: 1fr; }
        }