The Python viewer's appearance — interface theme, background color and toolbar layout — is set through its options object.

Set the theme and appearance options.
viewer = StiViewer()

viewer.options.appearance.theme = enums.StiViewerTheme.OFFICE_2022_BLACK_GREEN
viewer.options.appearance.backgroundColor = 'black'
viewer.options.toolbar.displayMode = enums.StiToolbarDisplayMode.SEPARATED

How it works. The options object drives the viewer's look, so a couple of assignments reskin the entire preview.

Hi. Need any help?