I claim the ornamental design for a cosmetic holder, as shown and described.
FIG. 1 is a front perspective view of my new and original ornamental design for a cosmetic holder, wherein the rear perspective view is a mirror image of the front perspective view shown;
FIG. 2 is a front elevation view thereof, wherein the rear elevation view is a mirror image of the front elevation view shown; and,
FIG. 3 is a top plan view thereof.
Portions of the design that are not shown in the drawings form no part of the claimed design. The broken lines that illustrate the interior and the lower portions of the cosmetic holder form no part of the claimed design.