Is the file "gianni_custom2.css" downloaded from iCloud?

Are you using public key authentication or user/password auth? It looks like the credentials are wrong. Do you get any other error message alert?

This is a bug in iOS 9. A reboot of your iPad Pro should fix that.

Are you sure that this is a problem of the editor? In the screenshot it looks like "<script></script>" is correctly highlighted as a string.

Or do you mean when you preview the file in the browser?

It makes no sense for Textastic to tell the system that it can open all file types like images, office documents or video files since Textastic can only edit plain text files.

This is the same behavior as in other apps like TextEdit or Xcode, so for me, it behaves as expected.

Textastic uses the system-provided font sizes and folder icons. I do not plan to change that at the moment, sorry.