Ext Grid does not display headers

[Mandeep]

I am upgrading my Ext 4.1 grid to Ext 6.2.1 but my headers are not getting displayed at the top. All I see is rows. I am using viewport to display the grid but still I see white space at the bottom and bottom scrollbar of the grid is in the middle of the screen. I am not using cmd and have imported following style sheet file.
ext621/build/classic/theme-classic/resources/theme-classic-all.css

Any help would be greatly appreciated.

[Gary Schlosberg]

That's odd. I'm guessing you don't have the header config set to false. Can you post your grid config?