:root {
            --primary-color: #3498db;
            --secondary-color: #2980b9;
            --accent-color: #e74c3c;
            --light-bg: #f8f9fa;
            --dark-bg: #343a40;
        }
        
        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background-color: #f5f5f5;
        }
        
        .navbar-brand {
            font-weight: 700;
            color: var(--primary-color) !important;
        }
        
        .hero-section {
            background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
            color: white;
            padding: 80px 0;
            margin-bottom: 30px;
        }
        
        .course-card {
            transition: transform 0.3s, box-shadow 0.3s;
            margin-bottom: 20px;
            border: none;
            border-radius: 10px;
            overflow: hidden;
        }
        
        .course-card:hover {
            transform: translateY(-5px);
            box-shadow: 0 10px 20px rgba(0, 0, 0, 0.1);
        }
        
        .course-card .card-img-top {
            height: 180px;
            object-fit: cover;
        }
        
        .progress {
            height: 10px;
            border-radius: 5px;
        }
        
        .feature-icon {
            background-color: var(--light-bg);
            color: var(--primary-color);
            width: 60px;
            height: 60px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 24px;
            margin-bottom: 15px;
        }
        
        .footer {
            background-color: var(--dark-bg);
            color: white;
            padding: 40px 0 20px;
            margin-top: 50px;
        }
        
        .nav-pills .nav-link.active {
            background-color: var(--primary-color);
        }
        
        .lesson-sidebar {
            position: sticky;
            top: 20px;
        }
        
        .quiz-card {
            border-left: 4px solid var(--primary-color);
        }
        
        .certificate-badge {
            width: 120px;
            height: 120px;
            background-color: var(--primary-color);
            color: white;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            margin: 0 auto 20px;
        }
        
        #backToTop {
            position: fixed;
            bottom: 20px;
            right: 20px;
            display: none;
            width: 40px;
            height: 40px;
            background-color: var(--primary-color);
            color: white;
            border-radius: 50%;
            text-align: center;
            line-height: 40px;
            z-index: 999;
        }
        .no-style {
            color: inherit; /* Kế thừa màu từ thẻ cha, ví dụ từ <h5> */
            text-decoration: none; /* Bỏ gạch chân */
          }

          .course-progress {
            margin: 20px 0;
        }
        
        .progress-bar {
            height: 20px;
            background-color: #f3f3f3;
            border-radius: 10px;
            overflow: hidden;
            position: relative;
        }
        
        .progress-fill {
            height: 100%;
            background-color: #4caf50;
            transition: width 0.5s ease;
        }
        
        .progress-text {
            margin-top: 5px;
            text-align: center;
            font-weight: bold;
        }
        
        .btn-completed {
            background-color: #4caf50;
            border-color: #4caf50;
        }
        
        .lesson-list .completed {
            position: relative;
        }
        
        .lesson-list .completed:before {
            content: '✓';
            position: absolute;
            left: -20px;
            color: #4caf50;
            font-weight: bold;
        }