我得到一个vaadin项目，看起来像这样：

package com.example.myapplication;

import com.vaadin.annotations.StyleSheet;
import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.server.VaadinRequest;
import com.vaadin.server.VaadinServlet;
import com.vaadin.shared.ui.label.LabelState;
import com.vaadin.ui.Button;
import com.vaadin.ui.Grid;
import com.vaadin.ui.Label;

@StyleSheet ("stylesheet.css")

@Theme("mytheme")
public class MyUI extends UI {

    private static final long serialVersionUID = 1L;

    @Override
    protected void init(VaadinRequest vaadinRequest) {
            Label lb = new Label("VAADIN PROJECT");
            lb.setStyleName("mystyle");
            layout.addComponent(lb);
            setContent(layout);

    }
    @WebServlet(urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true)
    @VaadinServletConfiguration(ui = MyUI.class, productionMode = false)
    public static class MyUIServlet extends VaadinServlet {
    }
}

以及与主文件位于同一目录中的.css文件：

.mystyle {
    color: red;
    font-size: 180px;
    pading-left: 30px;
}

当我试图运行项目时，它只打印文本，没有更多的更改。我该怎么修？我的结果