Maintaining length to width ratio while scaling GUI's (GUI.matrix )? help

how do i maintain the Length to width ratio of any GUI button while scaling i just need an explanation for all the parts of this code and i will be fine what do the parts of this function mean

GUI.matrix = Matrix4x4.TRS (Vector3(0, 0, 0), Quaternion.identity, Vector3 (0, 0, 1));