The ornamental design for a shower base, as shown and described.
In a preferred embodiment, the nature of this product is as a shower receptor for a shower plumbing fixture.
FIG. 1 is a top, right, front perspective view of a shower base of my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a right side elevational view thereof; and,
FIG. 5 is a top plan view of a shower base according to another embodiment thereof, the other views of which are mirror images of the respective views shown in FIGS. 1, 3 and 4.
The broken line representations in the figures are for the purpose of illustration only, and form no part of the claimed design.