How do I customize the title bar of a popup in a chrome extension?

Question

How do i style the title bar of a popup in a chrome extension? I notice this being done by Chat for Chrome. (Note: the screenshot for that one is outdated)

I got as

Answer 1

The window in the screenshot you show does have the title bar in the HTML/CSS.

Answer 2

Turns out that this isn't a regular chrome extension I was looking at. It's a chrome packaged app. And it's possible to remove the title bars with chrome apps.

Answer 3

I have been researching this topic much and I surely know that Hangouts is a extension, not a packaged app.

I believe the extension windows are modified desktop notifications. I go to create an extension using these modified desktop notifications and i will report the result here.