Style Issue

the style isn't changed when I change text size or background color, nothing happen.

You have to set the options={options} value within the Timer or Stopwatch Component.
Then you have to create a const containing the predefined attributes. Here is a working example:

const options = {
  container: {
    backgroundColor: '#FF0000',
    padding: 5,
    borderRadius: 5,
    width: 200,
    alignItems:'center',
  },
  text: {
    fontSize: 25,
    color: '#FFF',
    marginLeft: 7,
  }
};