The ornamental design for an ultrathindimmableled recess flat panel retrofit light, as shown and described.
FIG. 1 is a perspective view of the ultrathin dimmable LED recess flat panel retrofit light showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right elevation view thereof;
FIG. 5 is a left elevation view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a top plan view thereof.
Broken lines are included for depicting environmental subject matter as well as portions of the design not claimed, and form no part of the claimed design.