当我在Tomcat服务器上运行项目时，它显示此错误：
加载主题时出错，找不到“ primefaces-start”库的“ theme.css”资源
这是堆栈跟踪：
javax.servlet.ServletException: Error loading theme, cannot find "theme.css" resource of "primefaces-start" library
javax.faces.webapp.FacesServlet.service(FacesServlet.java:321)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
root cause
javax.faces.FacesException: Error loading theme, cannot find "theme.css" resource of "primefaces-start" library
org.primefaces.renderkit.HeadRenderer.encodeTheme(HeadRenderer.java:130)
org.primefaces.renderkit.HeadRenderer.encodeBegin(HeadRenderer.java:92)
javax.faces.component.UIComponentBase.encodeBegin(UIComponentBase.java:824)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1641)
javax.faces.component.UIComponent.encodeAll(UIComponent.java:1646)
com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:389)
com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:127)
com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:117)
com.sun.faces.lifecycle.Phase.doPhase(Phase.java:97)
com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:135)
javax.faces.webapp.FacesServlet.service(FacesServlet.java:309)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
这是怎么引起的，我该如何解决？