body { background-color: #f3f4f6; font-family: 'Plus Jakarta Sans', sans-serif; min-height: 100vh; display: flex; align-items: center; justify-content: center; padding: 20px; }
        .checkout-container { width: 100%; max-width: 950px; background: #ffffff; border-radius: 24px; overflow: hidden; box-shadow: 0 20px 50px rgba(0,0,0,0.1); display: flex; flex-wrap: wrap; }
        .summary-side { flex: 1; min-width: 320px; background: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%); padding: 40px; color: white; display: flex; flex-direction: column; justify-content: center; }
        .form-side { flex: 1.4; padding: 50px; background: #fff; color: #333; }
        .course-preview { background: rgba(255, 255, 255, 0.2); backdrop-filter: blur(10px); border-radius: 16px; padding: 20px; border: 1px solid rgba(255, 255, 255, 0.3); margin-bottom: 25px; text-align: center; }
        .course-img { width: 100%; border-radius: 12px; margin-bottom: 15px; box-shadow: 0 5px 15px rgba(0,0,0,0.2); }
        .price-tag { font-size: 2.5rem; font-weight: 800; color: #fff; }
        .form-control, .form-select { background: #f9fafb; border: 2px solid #e5e7eb; color: #111; border-radius: 12px; padding: 12px; font-weight: 500; }
        .btn-colorful { background: linear-gradient(to right, #4f46e5, #9333ea); color: white; font-weight: 700; border: none; padding: 15px; border-radius: 50px; width: 100%; font-size: 1rem; transition: 0.3s; box-shadow: 0 10px 20px rgba(79, 70, 229, 0.3); }
        .btn-colorful:hover { transform: translateY(-2px); box-shadow: 0 15px 30px rgba(79, 70, 229, 0.4); }
        @media (max-width: 768px) { .checkout-container { flex-direction: column; } }