body {
            background: linear-gradient(#4CAF50,#ff009d);
            min-height: 100vh;
            padding: 20px;
            font-family: Arial;
            margin: 0;
        }

        .back-btn {
            background-color: white;
            padding: 10px 20px;
            border-radius: 8px;
            text-decoration: none;
            color: #333;
            font-size: 18px;
            display: inline-block;
            margin-bottom: 20px;
        }

        .back-btn:hover {
            background-color: #f0f0f0;
        }

        .header {
            text-align: center;
            margin-bottom: 30px;
        }

        h1 {
            color: white;
            font-size: 40px;
        }

        .subtitle {
            color: white;
            font-size: 20px;
        }

        .score-box {
            text-align: center;
            margin-bottom: 30px;
        }

        .score {
            background-color: white;
            display: inline-block;
            padding: 15px 30px;
            border-radius: 10px;
            font-size: 24px;
        }

        .problem-box {
            background-color: white;
            max-width: 500px;
            margin: 0 auto;
            padding: 40px;
            border-radius: 15px;
            text-align: center;
        }

        .problem {
            font-size: 60px;
            margin-bottom: 30px;
            color: #4CAF50;
        }

        .answer-input {
            font-size: 40px;
            width: 150px;
            padding: 10px;
            text-align: center;
            border: 3px solid #4CAF50;
            border-radius: 8px;
        }

        .btn {
            font-size: 24px;
            padding: 15px 40px;
            border: none;
            border-radius: 8px;
            cursor: pointer;
            margin: 10px 5px;
        }

        .btn-check {
            background-color: #4CAF50;
            color: white;
        }

        .btn-new {
            background-color: #FF9800;
            color: white;
        }

        .btn:hover {
            opacity: 0.8;
        }

        .message {
            margin-top: 30px;
            font-size: 28px;
            font-weight: bold;
        }

        .correct {
            color: green;
        }

        .incorrect {
            color: red;
        }

        .hint {
            text-align: center;
            margin-top: 40px;
            color: white;
            font-size: 18px;
        }