/* CSS STYLES */
        :root {
            --primary-color: #007bff;
            --primary-hover: #0056b3;
            --secondary-color: #28a745;
            --secondary-hover: #218838;
            --danger-color: #dc3545;
            --danger-hover: #c82333;
            --light-bg: #f8f9fa;
            --white-bg: #ffffff;
            --border-color: #dee2e6;
            --text-color: #212529;
            --header-bg: #343a40;
        }

        body {
            font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
            background-color: #f0f2f5;
            margin: 0;
            color: var(--text-color);
        }

        .container {
            max-width: 1400px;
            margin: 0 auto;
            padding: 20px;
        }

        header {
            background-color: var(--header-bg);
            color: white;
            padding: 15px 25px;
            border-radius: 12px;
            margin-bottom: 25px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
        }

        header h1 { margin: 0; font-size: 1.8em; }

        nav a {
            color: white; text-decoration: none; margin-left: 15px; font-size: 1.1em;
            padding: 10px 15px; border-radius: 8px; transition: background-color 0.3s; cursor: pointer;
        }
        nav a:hover, nav a.active { background-color: var(--primary-color); }

        .page { display: none; }
        .page.active { display: block; }
        
        .main-content { display: grid; gap: 25px; }
        .single-column { grid-template-columns: 1fr; }
        .two-column { grid-template-columns: 2fr 1fr; }

        .panel {
            border: 1px solid var(--border-color); padding: 25px; border-radius: 12px;
            background: var(--white-bg); box-shadow: 0 2px 8px rgba(0,0,0,0.05);
        }

        h2 {
            font-size: 1.6em; color: var(--text-color); border-bottom: 2px solid var(--border-color);
            padding-bottom: 10px; margin-top: 0; margin-bottom: 20px;
        }

        .form-group { margin-bottom: 20px; }
        label { display: block; margin-bottom: 8px; font-weight: 600; }
        input, textarea, select {
            width: 100%; padding: 12px; border: 1px solid var(--border-color);
            border-radius: 8px; box-sizing: border-box; font-size: 1em;
        }

        button {
            padding: 12px 20px; color: white; border: none; border-radius: 8px;
            cursor: pointer; font-size: 1em; font-weight: 600; transition: background-color 0.2s, transform 0.1s;
        }
        button:active { transform: scale(0.98); }
        
        .btn { width: 100%; }
        .btn-primary { background-color: var(--primary-color); }
        .btn-primary:hover { background-color: var(--primary-hover); }
        .btn-secondary { background-color: var(--secondary-color); }
        .btn-secondary:hover { background-color: var(--secondary-hover); }
        .btn-danger { background-color: var(--danger-color); }
        .btn-danger:hover { background-color: var(--danger-hover); }

        table { width: 100%; border-collapse: collapse; }
        th, td { padding: 12px; border: 1px solid var(--border-color); text-align: left; }
        th { background-color: var(--light-bg); }
        .text-right { text-align: right; }

        .bill-total { font-size: 1.8em; font-weight: bold; color: var(--secondary-color); }
        #transactionList { list-style: none; padding: 0; max-height: 500px; overflow-y: auto; }
        #transactionList li {
            padding: 12px; border-bottom: 1px solid var(--border-color);
            display: flex; justify-content: space-between; align-items: center; cursor: pointer;
        }
        #transactionList li:hover { background-color: #e9ecef; }
        #transactionList li .delete-bill-btn {
            padding: 5px 10px;
            font-size: 0.8em;
            margin-left: 10px;
            width: auto; /* Override default btn width */
        }

        /* --- PRINT STYLES --- */
        #print-area { display: none; } /* Hidden by default */

        @media print {
            /* Hide the main application when printing */
            body > .container {
                display: none;
            }
            /* Show only the print area */
            body > #print-area {
                display: block;
            }
        }

        @media (max-width: 992px) {
            .two-column { grid-template-columns: 1fr; }
            header { flex-direction: column; align-items: flex-start; }
            nav { margin-top: 15px; width: 100%; display: flex; justify-content: flex-start; }
            nav a { margin: 0 10px 0 0; }
        }

        /* Styles for trial ended overlay */
        #trialEndedOverlay {
            display: none; /* Hidden by default */
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background-color: rgba(0, 0, 0, 0.8);
            color: white;
            z-index: 1000;
            justify-content: center;
            align-items: center;
            flex-direction: column;
            text-align: center;
        }
        #trialEndedOverlay h2 {
            font-size: 2.5em;
            margin-bottom: 20px;
            color: white; /* Override default h2 color */
            border-bottom: none; /* Remove border */
        }
        #trialEndedOverlay p {
            font-size: 1.2em;
            margin-bottom: 30px;
        }
        #trialEndedOverlay a.btn {
            display: inline-block;
            width: auto; /* Override 100% width */
            padding: 15px 30px;
            font-size: 1.5em;
            text-decoration: none;
            background-color: var(--primary-color);
            border-radius: 8px;
            transition: background-color 0.3s;
        }
        #trialEndedOverlay a.btn:hover {
            background-color: var(--primary-hover);
        }