The ornamental design for a lid for a container, as shown and described.
FIG. 1 is a top, front, left perspective view of a lid for a container showing my new design in a condition of use;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines in the drawings depict portions of the lid for a container that form no part of the claimed design. The broken lines showing a container in the drawings depict environmental matter that forms no part of the claimed design.