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 to prevent jumping on small screens */
            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%; /* Responsive width */
            width: auto; /* Let content determine width */
            display: flex;
            flex-direction: column;
            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;
        }
        .action-button {
            background-color: #4f46e5; /* Indigo */
            color: white;
            padding: 15px 30px;
            border-radius: 0; /* Square 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%; /* Make buttons fill container */
        }
        .action-button:hover {
            background-color: #4338ca; /* Darker indigo */
            transform: translateY(-1px);
        }
        .action-button:active {
            transform: translateY(1px);
            box-shadow: none;
        }
        .action-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: 24px; /* Prevent layout shift */
            text-align: center;
        }
        .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;
            vertical-align: middle;
            margin-right: 8px;
        }
        @keyframes spin {
            0% { transform: rotate(0deg); }
            100% { transform: rotate(360deg); }
        }