* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        :root {
            --bg-dark: #2b2b2b;
            --bg-medium: #3a3a3a;
            --bg-light: #4a4a4a;
            --border-color: #555;
            --text-primary: #e0e0e0;
            --text-secondary: #999;
            --accent-blue: #4a90e2;
            --accent-green: #5cb85c;
            --accent-red: #d9534f;
            --hover-bg: #505050;
            --input-bg: #353535;
            --table-header: #404040;
        }

        body {
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            background: var(--bg-dark);
            color: var(--text-primary);
            overflow: hidden;
            height: 100vh;
        }

        /* Top Menu Bar */
        .top-menu {
            background: var(--bg-medium);
            height: 40px;
            display: flex;
            align-items: center;
            padding: 0 10px;
            border-bottom: 1px solid var(--border-color);
            gap: 5px;
        }

        .menu-item {
            padding: 8px 15px;
            cursor: pointer;
            border-radius: 3px;
            font-size: 13px;
            transition: background 0.2s;
            position: relative;
        }

        .menu-item:hover {
            background: var(--hover-bg);
        }

        /* Dropdown Menu */
        .menu-item.dropdown {
            position: relative;
        }

        .dropdown-content {
            display: none;
            position: absolute;
            top: 100%;
            left: 0;
            background: var(--bg-light);
            border: 1px solid var(--border-color);
            border-radius: 3px;
            box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
            min-width: 200px;
            z-index: 1000;
            margin-top: 2px;
            padding-top: 3px;
        }

        .dropdown:hover .dropdown-content {
            display: block;
        }

        /* Invisible bridge between menu and dropdown to keep hover active */
        .dropdown::after {
            content: '';
            position: absolute;
            top: 100%;
            left: 0;
            right: 0;
            height: 5px;
        }

        .dropdown-item {
            padding: 10px 15px;
            cursor: pointer;
            font-size: 13px;
            display: flex;
            align-items: center;
            gap: 10px;
            transition: background 0.2s;
            border-bottom: 1px solid var(--border-color);
        }

        .dropdown-item:last-child {
            border-bottom: none;
        }

        .dropdown-item:hover {
            background: var(--hover-bg);
        }

        .dropdown-item i {
            width: 16px;
            text-align: center;
        }

        /* Main Container */
        .main-container {
            display: flex;
            height: calc(100vh - 40px);
        }

        /* Left Sidebar - Tree Menu */
        .sidebar {
            width: 250px;
            min-width: 250px;
            background: var(--bg-medium);
            border-right: 1px solid var(--border-color);
            overflow-y: auto;
            padding: 10px 0;
            transition: min-width 0.3s ease, width 0.3s ease;
        }

        .sidebar.collapsed {
            width: 0;
            min-width: 0;
            padding: 0;
            border-right: none;
            overflow: hidden;
        }

        .tree-item {
            padding: 8px 15px;
            cursor: pointer;
            display: flex;
            align-items: center;
            gap: 8px;
            font-size: 13px;
            transition: background 0.2s;
            user-select: none;
            text-decoration: none;
            color: inherit;
        }

        .tree-item:hover {
            background: var(--hover-bg);
        }

        .tree-item.active {
            background: var(--accent-blue);
            color: white;
        }

        .tree-item i {
            width: 16px;
            font-size: 12px;
        }

        .tree-children {
            padding-left: 20px;
        }

        /* Content Area */
        .content-area {
            flex: 1;
            display: flex;
            flex-direction: column;
            background: var(--bg-dark);
            overflow-y: auto;
        }

        /* Toolbar */
        .toolbar {
            background: var(--bg-medium);
            padding: 8px 15px;
            border-bottom: 1px solid var(--border-color);
            display: flex;
            gap: 10px;
            align-items: center;
        }

        .btn {
            padding: 6px 15px;
            background: var(--bg-light);
            border: 1px solid var(--border-color);
            color: var(--text-primary);
            border-radius: 3px;
            cursor: pointer;
            font-size: 13px;
            display: inline-flex;
            align-items: center;
            gap: 6px;
            transition: all 0.2s;
        }

        .btn:hover {
            background: var(--hover-bg);
            border-color: var(--accent-blue);
        }

        .btn-primary {
            background: var(--accent-blue);
            border-color: var(--accent-blue);
            color: white;
        }

        .btn-primary:hover {
            background: #357abd;
        }

        .btn-success {
            background: var(--accent-green);
            border-color: var(--accent-green);
            color: white;
        }

        .btn-danger {
            background: var(--accent-red);
            border-color: var(--accent-red);
            color: white;
        }

        /* Search/Filter Bar */
        .filter-bar {
            background: var(--bg-medium);
            padding: 10px 15px;
            border-bottom: 1px solid var(--border-color);
            display: flex;
            gap: 10px;
            align-items: center;
        }

        .input-group {
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .input-group label {
            font-size: 12px;
            color: var(--text-secondary);
            white-space: nowrap;
        }

        input,
        select {
            background: var(--input-bg);
            border: 1px solid var(--border-color);
            color: var(--text-primary);
            padding: 5px 10px;
            border-radius: 3px;
            font-size: 13px;
        }

        input:focus,
        select:focus {
            outline: none;
            border-color: var(--accent-blue);
        }

        /* Data Table */
        .data-table-container {
            flex: 1;
            overflow: auto;
            padding: 15px;
        }

        .data-table {
            width: 100%;
            border-collapse: collapse;
            font-size: 12px;
        }

        .data-table thead {
            position: sticky;
            top: 0;
            background: var(--table-header);
            z-index: 10;
        }

        .data-table th {
            padding: 8px 12px;
            text-align: left;
            border: 1px solid var(--border-color);
            font-weight: 600;
            color: var(--text-primary);
            white-space: nowrap;
        }

        .data-table td {
            padding: 6px 12px;
            border: 1px solid var(--border-color);
            white-space: nowrap;
        }

        .data-table tbody tr:hover {
            background: var(--hover-bg);
        }

        .data-table tbody tr.selected {
            background: rgba(74, 144, 226, 0.3);
        }

        /* Document Form - Three Column Layout */
        .document-form {
            display: grid;
            grid-template-columns: 350px 1fr 300px;
            gap: 15px;
            padding: 15px;
            overflow-y: auto;
            flex: 1;
        }

        .form-panel {
            background: var(--bg-medium);
            border: 1px solid var(--border-color);
            border-radius: 4px;
            padding: 15px;
        }

        .form-panel h3 {
            font-size: 14px;
            margin-bottom: 15px;
            padding-bottom: 8px;
            border-bottom: 1px solid var(--border-color);
        }

        .form-group {
            margin-bottom: 12px;
        }

        .form-group label {
            display: block;
            font-size: 11px;
            color: var(--text-secondary);
            margin-bottom: 4px;
        }

        .form-group input,
        .form-group select,
        .form-group textarea {
            width: 100%;
        }

        textarea {
            background: var(--input-bg);
            border: 1px solid var(--border-color);
            color: var(--text-primary);
            padding: 8px;
            border-radius: 3px;
            font-size: 13px;
            font-family: inherit;
            resize: vertical;
        }

        /* Items Table in Document */
        .items-section {
            grid-column: 1 / -1;
            background: var(--bg-medium);
            border: 1px solid var(--border-color);
            border-radius: 4px;
            padding: 15px;
        }

        .items-toolbar {
            display: flex;
            gap: 10px;
            margin-bottom: 10px;
        }

        .items-table {
            width: 100%;
            border-collapse: collapse;
            font-size: 12px;
        }

        .items-table th,
        .items-table td {
            padding: 6px 8px;
            border: 1px solid var(--border-color);
            text-align: left;
        }

        .items-table th {
            background: var(--table-header);
            font-weight: 600;
        }

        .items-table input {
            width: 100%;
            padding: 4px 6px;
        }

        /* Modal */
        .modal {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: rgba(0, 0, 0, 0.7);
            z-index: 1000;
            align-items: center;
            justify-content: center;
        }

        .modal.show {
            display: flex;
        }

        .modal-content {
            background: var(--bg-medium);
            border: 1px solid var(--border-color);
            border-radius: 4px;
            width: 90%;
            max-width: 1200px;
            max-height: 80vh;
            display: flex;
            flex-direction: column;
        }

        .modal-header {
            padding: 15px;
            border-bottom: 1px solid var(--border-color);
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .modal-header h2 {
            font-size: 16px;
        }

        .modal-body {
            padding: 15px;
            overflow-y: auto;
            flex: 1;
        }

        .modal-footer {
            padding: 15px;
            border-top: 1px solid var(--border-color);
            display: flex;
            justify-content: flex-end;
            gap: 10px;
        }

        /* Status Bar */
        .status-bar {
            background: var(--bg-medium);
            height: 30px;
            border-top: 1px solid var(--border-color);
            display: flex;
            align-items: center;
            padding: 0 15px;
            font-size: 11px;
            color: var(--text-secondary);
            gap: 20px;
        }

        /* Summary Box in Document */
        .summary-box {
            background: var(--input-bg);
            border: 1px solid var(--border-color);
            border-radius: 4px;
            padding: 12px;
            margin-top: 15px;
        }

        .summary-row {
            display: flex;
            justify-content: space-between;
            padding: 5px 0;
            font-size: 13px;
        }

        .summary-row.total {
            font-size: 16px;
            font-weight: bold;
            color: var(--accent-blue);
            border-top: 2px solid var(--border-color);
            padding-top: 10px;
            margin-top: 5px;
        }

        /* Scrollbar Styling */
        ::-webkit-scrollbar {
            width: 12px;
            height: 12px;
        }

        ::-webkit-scrollbar-track {
            background: var(--bg-dark);
        }

        ::-webkit-scrollbar-thumb {
            background: var(--bg-light);
            border-radius: 6px;
        }

        ::-webkit-scrollbar-thumb:hover {
            background: var(--hover-bg);
        }

        /* Loading Spinner */
        .spinner {
            border: 3px solid var(--bg-light);
            border-top: 3px solid var(--accent-blue);
            border-radius: 50%;
            width: 40px;
            height: 40px;
            animation: spin 1s linear infinite;
            margin: 50px auto;
        }

        @keyframes spin {
            0% {
                transform: rotate(0deg);
            }

            100% {
                transform: rotate(360deg);
            }
        }

        .loading-container {
            display: flex;
            justify-content: center;
            align-items: center;
            padding: 50px;
        }