A notable technical element used would be the use of deep focus and lighting/shadows to produce an effect that progressively shows Kane’s loss of control and decent into darkness. The deep focus technique works in combination with lighting, composition and camera angle to create the desired effect. Deep focus is most effective when Kane is seen to be no longer in control of his situation and space because it provides the audience with a clear view of when Kane has control, and when he lacks power. With the addition of the use of Welles lighting the end product was that to of a Noir film style, which is associated with dark, moody and mysterious environments to create a tense atmosphere within a scene.

ref: https://www.sparknotes.com/film/citizenkane/section2/