member 30 includes a main body 31 a plurality of sliding slots 312 are defined in a bottom portion of the main body 31 corresponding to the sliding rails 119 of the first panel 11 and a plurality of sliding slots 314 are defined in a top portion of the main body 31 corresponding to the sliding rails of the second panel 13 the main body 31 includes a front surface 311 and a notch 313 is defined by cutting into a middle portion of the front surface 311 corresponding to the post 114 of the first panel 11 a groove 315 is defined in a middle section of the top portion of the main body 31 in communication with the notch 313 and a slanted surface 317 adjoining the groove 315 is defined between the front surface 311 and a rear surface of the main body 31 a pair of hooks 32 respectively having a hooking portion 321 protrude from the top portion of the main body 31 corresponding to the through holes 131 of the second panel 13 a first rod 33 and a second rod 34 extend from two opposite ends of the main body 31 respectively the base unit 50 defines a pair of latching slots 51 corresponding to the hooks 32 of the latching member 30 referring also to fig2 and 3 in assembly the elastic member 40 is.