buttonstyle.js

const styles = StyleSheet.create({
  box: {
    backgroundColor: "blue",
    padding: 20,
    borderRadius: 50
  },
  text: {
    color: "white",
    fontSize: 20
  }
});
class Button extends React.Component {
  render() {
    return (
      <TouchableOpacity style={styles.box}>
         <Text style={styles.text}>
           {this.props.title}
         </Text>
      </TouchableOpacity>
    );
  }
}