User interface designers are particular about how the product is laid out. They are in charge of designing each screen or page with which a user interacts ensuring that the UI visually communicates the path that a UX developer has laid out.

UI designers are also typically responsible for creating and/or implementing a cohesive style guide and ensuring that a consistent design language is applied across the product.

Maintaining consistency in visual elements and defining visual behaviour also fall under the purview of a UI designer.