The ornamental design for a surface configuration of a hardtop for a vehicle, as shown and described.
FIG. 1 is a right, front perspective view of a surface configuration of a hardtop for a vehicle according to my novel design, the left, front perspective view being mirror symmetrical;
FIG. 2 is a right side view of the surface configuration of a hardtop for a vehicle according to my novel design, the left side view being mirror symmetrical;
FIG. 3 is a right, rear perspective view of the surface configuration of a hardtop for a vehicle according to my novel design, the left, rear perspective view being mirror symmetrical; and,
FIG. 4 is a top view of the surface configuration of a hardtop for a vehicle according to my novel design.
The dash lines included depict environment and are not part of the claimed design.