How to change styling of modal dialogue in google apps script

I want to change the position and background color of modal dialogue in google apps script for my addon I have searched a lot but only found answers using UiApp which is now deprecated and no longer works. I found no answers for doing this using HtmlService. Only available function in after createHtmlOutputFromFile('Index') are : setWidth and setHeight which work perfectly but i need to change position of modal too. Is there any way to do this at the moment?