each positioned between the first slot 20 and a second slot 22 and with the cross section shaped like a rectangle please then refer to fig1 to fig5 the decorative piece 14 comprises a first decorative piece 40 and two second decorative pieces 42 the first decorative piece 40 is of a pre determined length with its two rims curved outwards and the inside shaped like a dove tail slot forming the first interlocking part 40 a which can be interlocked with the first locking part 20 a the second decorative piece 42 is roughly l shaped with its two rims also curved outwards on the inner side of the second decorative piece 42 it forms a dovetail shaped second interlocking part 42 a facing the main body 39 s 12 side rims and a decorative piece locking part 42 b which is a protruding column with one end shaped like a hook facing the main body 39 s 12 front rim again please refer to fig1 to fig5 when assembling the user first push the first decorative piece 40 from one end of the connecting slot 24 into the first slot 20 with the inner side of the first decorative piece 40 covering the whole area of.