Chair backrest

FIG. 1 is a perspective view of a chair backrest showing my new design;

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;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is another perspective view thereof.

The broken line showing of the chair backrest is for the purpose of illustrating portions of the article and forms no part of the claimed design.