Creating App for Android and Ios

Hi guys I want to create app for android and IOS in ionic. I am not getting from where to start. I have the knowledge of Angularjs ,javascript ,html ,css ND I have also developed one Ionic app for IOS and android separately now I want make it through only one code base.

Can anyone suggest me the structure of Ionic for android and IOS?
How can we design custom UI in ionic ?
How to write css for Android devices and IOS ,is it handled by Ionic or we have to wright media query for each device.(In my previous app I have written separate media query for each resolution)?

Can we do Android and IOS app through only one codebase?

I am using Ionic 1?