Both parts are solid. Print them both with 0% infil and no top layers. Be sure to set the variables at the top of the file to match your needs and printer. wall_thickness assumes walls are 2 lines thick for a 0.4mm nozzle.
To print 'pot_lid();', turn it up the other way on the print bed so that the top lip is on the bed. Print the lid at 101% scale for a super snug fit (where the lid doesn't fall off). Otherwise, print at 100% scale for an OK fit that falls off if inverted (but doesn't scratch).