ragsna wrote: The preview window does not open in a blank window.
That is odd; I am using v.2.0.1 of the plug-in, and the preview window opens in its own separate window for me.
ragsna wrote: There is the layout from the "Main" Forum window inside. Normally I would like to have a blank, white background only in the preview window, just like here tested.
Option 1 - the quick and dirty way:
Open the template file for the plug-in (i.e. addon_preview2.html located in your miniBB's templates directory) in a plain text editor, change <body class="gbody"> to <body>, save and then upload the updated file.
Edit your forum's stylesheet and either update .gbody or create a new class just for the preview window.
All best -