How to display A Form dialog box at the top middle in Browser UI

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Hi,

We Have a requirement where on click of a button we need to invoke Form Dialog box as popup asking to enter the first name and last name, and that should appear on the top middle of my report screen on BROWSER UI,

But because of the object extension that is being added in the workspace in agent desktop, we are just able to change the position in that area only where  the extension has been added for eg(if I add the extension at bottom of all my fields, I am able to change the dialog css properties within the extension area)