content: 
  import React, { Component } from 'react';
  import { Text, View, TouchableOpacity } from 'react-native';
  
  class Header extends Component {
  
      renderBackButton() {
          if(this.props.backButtonText) {
              return (
                  <TouchableOpacity 
                      onPress={() => this.props.onBackButtonTap()} 
                      style={styles.backButtonStyle}
                  >
                      <Text>
                          {this.props.backButtonText}
                      </Text>
                  </TouchableOpacity>
              );
          }
      }
  
      render() {
          const { textStyle, viewStyle } = styles;
          return (
              <View style={viewStyle}>
                  {this.renderBackButton()}
                  <Text style={textStyle}>
                      {this.props.children}
                  </Text>
              </View>
          )
      }
  }
  
  const styles = {
      viewStyle: {
          backgroundColor: '#F8F8F8',
          justifyContent: 'center',
          alignItems: 'center',
          height: 60,
          paddingTop: 15,
          shadowColor: '#000',
          shadowOffset: { width: 0, height: 2},
          shadowOpacity: 0.2,
          elevation: 2,
          position: 'relative',
          flexDirection: 'row'
      },
      textStyle: {
          fontSize: 20,
          textAlign: 'center',
          flex: 1
      },
      backButtonStyle: {
          paddingLeft: 10,
          paddingRight: 20
      }
  }
  
  export { Header };