/* CSS styles */
        body {
            font-family: Arial, sans-serif;
            margin: 0; /* Remove default margin */
        }

        h1 {
            text-align: center;
            margin-top: 20px;
        }

        #sudoku-container {
            max-width: 500px; /* Limit maximum width */
            margin: 0 auto;
            padding: 0 20px; /* 20px space on the sides */
            box-sizing: border-box; /* Include padding in width calculations */
        }

        #sudoku-grid {
            border-collapse: collapse;
            width: 100%;
            table-layout: fixed; /* Makes columns equal width */
        }

        #sudoku-grid td {
            border: 1px solid #000;
            width: 11.11%; /* 100% divided by 9 columns */
            position: relative;
            cursor: pointer;
            box-sizing: border-box;
            text-align: center;
            vertical-align: middle;
            font-size: 1.5em; /* Adjust font size as needed */
        }

        /* Ensure cells are square */
        #sudoku-grid td:before {
            content: "";
            display: block;
            padding-top: 100%; /* Makes the height equal to the width */
        }

        #sudoku-grid td > div {
            position: absolute;
            top: 0;
            left: 0;
            right: 0;
            bottom: 0;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        /* Thick borders for 3x3 boxes */
        .thick-border-left {
            border-left: 3px solid #000 !important;
        }

        .thick-border-right {
            border-right: 3px solid #000 !important;
        }

        .thick-border-top {
            border-top: 3px solid #000 !important;
        }

        .thick-border-bottom {
            border-bottom: 3px solid #000 !important;
        }

        /* Colors for correct and incorrect lines */
        .correct {
            background-color: #d4edda !important; /* Light green */
        }

        .incorrect {
            background-color: #f8d7da !important; /* Light red */
        }

        /* Style for the number panel */
        #number-panel {
            position: absolute;
            background-color: #e0e0e0;
            border: 1px solid #000;
            display: none;
            z-index: 100;
            padding: 5px;
        }

        #number-panel .number-buttons {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            grid-gap: 5px;
        }

        #number-panel button {
            width: 50px;
            height: 50px;
            font-size: 18px;
            margin: 0;
            padding: 0;
            border: 1px solid #000;
            background-color: #dddddd;
            cursor: pointer;
        }

        #number-panel button:hover {
            background-color: #aaaaaa;
        }

        /* Style for delete button */
        #number-panel .delete-button {
            position: absolute;
            top: -15px;
            right: -15px;
            width: 30px;
            height: 30px;
            background-color: red;
            color: white;
            font-size: 20px;
            border: 1px solid #000;
            border-radius: 50%;
            cursor: pointer;
            line-height: 28px;
            text-align: center;
        }

        /* Style for fixed numbers */
        .fixed {
            background-color: #e6f0ff; /* Light blue */
            font-weight: bold;
        }

        /* Style for difficulty buttons */
        #difficulty-buttons {
            text-align: center;
            margin-top: 20px;
            padding: 0 20px; /* 20px space on the sides */
            box-sizing: border-box;
        }

        #difficulty-buttons button {
            margin: 5px;
            padding: 10px 20px;
            font-size: 16px;
            cursor: pointer;
        }

        /* Active difficulty button style */
        #difficulty-buttons .active-difficulty {
            background-color: #d4edda; /* Light green */
        }

        /* Responsive adjustments */
        @media (max-width: 600px) {
            #number-panel button {
                width: 40px;
                height: 40px;
                font-size: 16px;
            }

            #number-panel .delete-button {
                width: 25px;
                height: 25px;
                font-size: 16px;
                line-height: 23px;
            }

            #difficulty-buttons button {
                padding: 8px 16px;
                font-size: 14px;
            }

            #sudoku-grid td {
                font-size: 1.2em;
            }
        }