How to set the whole app in android's style even if on ios in ionic2?

You can use:

@App({
  templateUrl: 'build/app.html',
  config: {
    mode: 'md'
  }
})

I'm not sure why this isn't documented, so I created an issue for it:

There is currently no way to set a single component to match the styles of a different platform, but you could override the iOS Sass variables to get close to that of Androids. If this is a feature you'd like - could you create an issue and we can discuss it? Thanks! http://ionicframework.com/submit-issue/