Customizing Mobile Input Field

Hi,

I wish to customize the mobile input field and was wondering how. I saw Hearthstone (made with Unity) customized their chat input field:

Is it possible to do such inside Unity, using Unity tools and scripting, or do I need to manipulate in Xcode? Also, was wondering how to change the "Return" key to "Send" and have it post/send the comment in. Would be great to also learn how to do that!