1.所有组件（component）都有一个 style 属性；

2.在一个地方使用 StyleSheet.Create 去给 style 下定义：

    例：

    const styles = StyleSheet.create({

                          bigblue: {

                                            color: 'blue',

                                            fontWeight: 'bold',

                                            fontSize: 30,

                                          },

                              red: {

                                            color: 'red',                

                                      },

                                });