body {
            font-family: 'Inter', sans-serif;
            background-color: #f0f4f8; /* Light blue-gray background */
            display: flex;
            justify-content: center;
            align-items: flex-start; /* Align to top */
            min-height: 100vh;
            padding: 20px;
            box-sizing: border-box;
        }
        #app-container {
            background-color: #ffffff;
            padding: 30px;
            border-radius: 15px;
            box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
            max-width: 95%;
            width: auto;
            display: flex;
            flex-direction: column;
            gap: 20px;
            align-items: center;
        }
        .form-group {
            display: flex;
            flex-direction: column;
            gap: 8px;
            width: 100%;
        }
        select {
            padding: 10px;
            border: 1px solid #cbd5e1;
            border-radius: 8px;
            background-color: #f8fafc;
            font-size: 1rem;
        }
        button {
            background-color: #4f46e5; /* Indigo */
            color: white;
            padding: 15px 30px;
            border-radius: 8px; /* Rounded corners */
            font-weight: 600;
            font-size: 1.1rem;
            transition: background-color 0.3s ease, transform 0.1s ease;
            cursor: pointer;
            box-shadow: 0 4px 10px rgba(79, 70, 229, 0.3);
            width: 100%;
        }
        button:hover {
            background-color: #6366f1; /* Lighter indigo */
            transform: translateY(-1px);
        }
        button:active {
            transform: translateY(1px);
            box-shadow: none;
        }
        button:disabled {
            background-color: #9ca3af;
            cursor: not-allowed;
            box-shadow: none;
        }
        #puzzleCanvas {
            border: 2px solid #e2e8f0;
            border-radius: 8px;
            background-color: #f8fafc;
        }
        #statusMessage {
            font-weight: 600;
            color: #475569; /* Slate gray */
            min-height: 48px; /* Increased height for two lines */
            text-align: center;
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
        }
        /* Spinner styles */
        .spinner {
            border: 4px solid rgba(0, 0, 0, 0.1);
            border-left-color: #4f46e5;
            border-radius: 50%;
            width: 24px;
            height: 24px;
            animation: spin 1s linear infinite;
            display: inline-block;
            margin-top: 8px;
        }
        @keyframes spin {
            0% { transform: rotate(0deg); }
            100% { transform: rotate(360deg); }
        }

        /* Simple Modal Styles */
        .modal {
            display: none; /* Hidden by default */
            position: fixed; /* Stay in place */
            z-index: 1000; /* Sit on top */
            left: 0;
            top: 0;
            width: 100%; /* Full width */
            height: 100%; /* Full height */
            overflow: auto; /* Enable scroll if needed */
            background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
            justify-content: center;
            align-items: center;
        }
        .modal-content {
            background-color: #fefefe;
            margin: auto;
            padding: 20px;
            border: 1px solid #888;
            width: 80%;
            max-width: 500px;
            border-radius: 1rem;
            box-shadow: 0 5px 15px rgba(0,0,0,0.3);
            text-align: center;
        }
        .close-button {
            color: #aaa;
            float: right;
            font-size: 28px;
            font-weight: bold;
        }
        .close-button:hover,
        .close-button:focus {
            color: black;
            text-decoration: none;
            cursor: pointer;
        }