Hello!
Why not a small window opens, and in full screen?


MainPanel class:
Code:
package ru.softded.main.client.Panel;

import com.extjs.gxt.ui.client.widget.ContentPanel;
import com.extjs.gxt.ui.client.widget.layout.FitLayout;
import ru.softded.main.client.Window.EmployeeWindow;


public class MainPanel extends ContentPanel {

    public MainPanel() {
        this.setLayout(new FitLayout());
        this.setHeaderVisible(false);
    }

    public void showEmployeeWindow() {
        EmployeeWindow employeeWindow = new EmployeeWindow();
        this.add(employeeWindow);
    }
}
EmployeeWindow class:

Code:
package ru.softded.main.client.Window;

import com.extjs.gxt.ui.client.event.ButtonEvent;
import com.extjs.gxt.ui.client.event.SelectionListener;
import com.extjs.gxt.ui.client.store.ListStore;
import com.extjs.gxt.ui.client.widget.Label;
import com.extjs.gxt.ui.client.widget.Window;
import com.extjs.gxt.ui.client.widget.button.Button;
import com.extjs.gxt.ui.client.widget.grid.ColumnConfig;
import com.extjs.gxt.ui.client.widget.grid.ColumnModel;
import com.extjs.gxt.ui.client.widget.grid.Grid;
import com.extjs.gxt.ui.client.widget.layout.AccordionLayout;
import com.extjs.gxt.ui.client.widget.layout.FitLayout;
import com.extjs.gxt.ui.client.widget.layout.FlowLayout;
import com.extjs.gxt.ui.client.widget.toolbar.ToolBar;
import com.google.gwt.user.client.Element;
import com.google.gwt.user.client.rpc.AsyncCallback;
import ru.softded.main.client.Forms.EmployeeForm;
import ru.softded.main.client.Model.EmployeeModel;
import ru.softded.main.client.Service.EmployeeService;
import ru.softded.main.shared.Employee;

import java.util.ArrayList;
import java.util.List;

public class EmployeeWindow extends Window {

    Grid<EmployeeModel> grid;

    public EmployeeWindow() {
        setLayout(new FitLayout());
        setWidth(650);
        setHeight(300);
        setHeading("Заказчики");
        setMaximizable(true);

        ToolBar toolBar = new ToolBar();
        final Button addButton = new Button("Добавить");
        addButton.setIconStyle("button-add");
        final Button editButton = new Button("Редактировать");
        editButton.setIconStyle("button-edit");
        final Button delButton = new Button("Удалить");
        delButton.setIconStyle("button-del");
//        final Button openButton = new Button("Открыть");
//        openButton.setIconStyle("button-open");
//        toolBar.add(openButton);
        toolBar.add(addButton);
        toolBar.add(editButton);
        toolBar.add(delButton);
        this.setTopComponent(toolBar);

        addButton.addSelectionListener(new SelectionListener<ButtonEvent>() {
            @Override
            public void componentSelected(ButtonEvent ce) {
                EmployeeForm employeeForm = new EmployeeForm();
                employeeForm.show();
            }
        });

        editButton.addSelectionListener(new SelectionListener<ButtonEvent>() {
            @Override
            public void componentSelected(ButtonEvent ce) {
                EmployeeModel employeeModel = grid.getSelectionModel().getSelectedItem();
                if (employeeModel != null) {
                    EmployeeForm employeeForm = new EmployeeForm(employeeModel);
                    employeeForm.show();
                }
            }
        });

        delButton.addSelectionListener(new SelectionListener<ButtonEvent>() {
            @Override
            public void componentSelected(ButtonEvent ce) {
                EmployeeModel employeeModel = grid.getSelectionModel().getSelectedItem();
                if (employeeModel != null) {
                    EmployeeService.App.getInstance().delEmployee(employeeModel, new AsyncCallback<Void>() {
                        public void onFailure(Throwable caught) {
                            com.google.gwt.user.client.Window.alert("Ошибка удаления");
                        }

                        public void onSuccess(Void result) {
                            com.google.gwt.user.client.Window.alert("Запись удалена");
                            grid.getStore().remove(grid.getSelectionModel().getSelectedItem());
                        }
                    });
                }
            }
        });


        final Label labelError = new Label();
        final ListStore<EmployeeModel> employeeModelListStore = new ListStore<EmployeeModel>();
        EmployeeService.App.getInstance().getAllEmployeeModels(new AsyncCallback<List<EmployeeModel>>() {
            public void onFailure(Throwable caught) {
                com.google.gwt.user.client.Window.alert(caught.getLocalizedMessage());
            }

            public void onSuccess(List<EmployeeModel> result) {
                employeeModelListStore.add(result);
            }
        });

        List<ColumnConfig> columnConfigs = new ArrayList<ColumnConfig>();

        ColumnConfig column = new ColumnConfig("name", "Название организации", 100);
        columnConfigs.add(column);

        column = new ColumnConfig("codeName", "Обозначение", 100);
        columnConfigs.add(column);

        column = new ColumnConfig("tel", "Телефон", 100);
        columnConfigs.add(column);

        column = new ColumnConfig("email", "Email", 100);
        columnConfigs.add(column);

        column = new ColumnConfig("login", "Логин", 100);
        columnConfigs.add(column);

        column = new ColumnConfig("pass", "Пароль", 100);
        columnConfigs.add(column);

        ColumnModel columnModel = new ColumnModel(columnConfigs);

        grid = new Grid<EmployeeModel>(employeeModelListStore, columnModel);
        grid.setBorders(true);
        grid.setAutoExpandColumn("name");
        grid.setStyleAttribute("border-Top", "none");
        grid.setStripeRows(true);

        add(grid);

    }
}
And AppView class:
Code:
    private void onCenterPanelReady(AppEvent event) {
        BorderLayoutData centerLayoutData = new BorderLayoutData(Style.LayoutRegion.CENTER);
        centerLayoutData.setCollapsible(true);
        Component component = event.getData();
        viewport.add(component, centerLayoutData);
    }