Code 1 : style et composants

import React from 'react';
import { StyleSheet, Text, View } from 'react-native';

export default function App() {
  return (
    <View style={styles.container}>
      <View style={styles.header}>
        <Text style={styles.headerText}>Mon journal de bord</Text>
      </View>

      <View style={styles.containerPadding}>
        <Text>Lorem ipsum !</Text>

        <View>
          <Text>Bienvenue dans mon journal de bord </Text>
        </View>

        <Text>
          Lorem ipsum dolor
        </Text>
        <Text>
          Lorem ipsum dolor
        </Text>
      </View>
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    paddingTop: 30,
    flex: 1,
    backgroundColor: '#fff',
  },
  containerPadding : {
    paddingHorizontal: 30,
    paddingTop: 10,
  },
  header : {
    // Layout
    width: '100%',
    height: 55,
    alignItems: "center",
    justifyContent: "center",
    // Style
    borderBottomColor: 'lightgrey',
    borderBottomWidth: 2,
  },
  headerText: {
    fontSize: 18,
    fontWeight: 'bold'
  }
});