You can set the background of the Corkboard to the cork texture again in File > Options > Appearance > Corkboard > Corkboard background. Pick the Corkboard Texture from the drop-down list.
I’ve forgotten how the 1.9-version looks. Scrivener 3.0 Themes have a color palette and a Stylesheet that work on the 3.x code only.
What would make version 3 look like 1.9?
Hope this helps