I have a similar dark theme. Unfortunately, the background colour of the pasteboard is not styleable separately from the colour of the page. You can use
Document Properties and "Background Colour" option to set a different colour, but it affects both the pasteboard and the page.
There is a workaround however. If you change the background to a grey colour in the Document Properties, you can add a rectangle filled white to cover the page - set the width and height same as the page dimensions, and the x and y co-ordinates to 0. Then lock that layer, perhaps rename it "Background", and add a new layer. Then you could save this as your default template. In Windows, save the document named default.svg in the folder at
Each time you open a new document or start the application, Inkscape will load the default.svg
The downside is if you choose a different page size, you will have to edit the white filled rectangle to match the new page size.