Which of the following best describes customization in Liferay?

Customization in Liferay primarily involves using themes and layout templates to enhance and modify the user interface. This process allows developers to create tailored experiences that align with specific business needs and branding requirements. Themes enable a change in appearance across the entire platform, while layout templates facilitate the organization of content and structure displayed on pages.

In contrast, altering backend configurations is often more technical and geared towards system administration rather than user experience. Implementing external plugins is an important aspect of Liferay's extensibility, but it doesn't fully capture the essence of customization in terms of visual and interface-level changes. Similarly, merely modifying CSS styles, while a part of the broader customization process, doesn't encompass the integration of styles, layouts, and functionalities that themes and layout templates provide. Thus, option B accurately encompasses the holistic approach to interface customization in Liferay.