The expressionist art movement was made to rebel against traditional bourgeois art which demanded aesthetic and culture, so art during this movement can not be distinguished by a singular style or method.
“German Expressionism art took inspiration from artists such as Edvard Munch, El Greco, and Vincent van Gogh. Artists were less concerned with producing work that held aesthetic value and instead focused on creating compositions that had the ability to emit powerful reactions when viewed. This was done by combining jagged brush marks, incongruous colours, and simplistic shapes, which were all authentic German Expressionism characteristics. Thus, the style created went against what was considered traditional art.”
“The Cabinet of Dr. Caligari is known for the skewed, anxiety-provoking angles that made up its painted backdrops, as well as its hauntingly gruesome storyline. Wiene hired Expressionist painters Hermann Warm and Walter Reimann to create the sets used in the background. The two artists wanted to challenge the formal techniques associated with Modernism and went on to use perception, absurd patterns, and rough lines to create a macabre world.
This film can be viewed as representing the absurdity displayed in the war, as Cesare is symbolic of the innocent soldiers who were forced to kill others under the control of the government, represented by Dr. Caligari. Thus, German Expressionism existed as the appropriate movement to help employ the sense of anxiety and uneasiness that was felt throughout Germany in the aftermath of World War One.”
Source: https://artincontext.org/german-expressionism/