Adding a new button style to @shoutem/theme

Question

I was able to get @Shoutem/theme working. I want to introduce a new button style along side all the others.

Here is my code.

const theme = Object.assign(UITheme(), {

  'shoutem.ui.Button': {

    '.new-button': {
    flex: 1,
    flexDirection: 'row',
    alignItems: 'center',
    justifyContent: 'center',
    backgroundColor: '#ffffff',
    borderRadius: 2,
    borderWidth: 1,
    borderColor:  '#cccccc',
    paddingTop: 9,
    paddingBottom: 9,
  }
}
});

With this code in place styleName="new-button" is the only button available.

How do I make it an addition and not a replacement?