A rectangular plate 80mm × 60mm × 8mm with a rectangular pocket milled into the top face: the pocket is 60mm × 40mm × 4mm deep and centered on the plate.
import cadquery as cq result = ( cq.Workplane("XY") .box(80, 60, 8) .faces(">Z").workplane() .rect(60, 40) .cutBlind(-4) )