What role do "CSS Variables" play in Liferay theming?

CSS variables, also known as custom properties, play a significant role in Liferay theming by allowing developers to define reusable values for styling. By utilizing CSS variables, developers can create a more maintainable and flexible styling system. When a CSS variable is defined, it can be reused throughout various stylesheets, making it easier to manage design changes. For example, if a particular color or sizing value is used multiple times across different components within a theme, assigning that value to a CSS variable means that any updates can be made in one centralized location rather than modifying each instance individually.

This capability not only streamlines the theming process but also enhances consistency throughout the user interface. Additionally, when CSS variables are used, changes to themes can be more dynamic, allowing users to adjust themes on-the-fly, which can lead to improved user experience.

The other choices, while important aspects of application development, do not pertain to the specific functionality of CSS variables in the context of theming. Handling user input validation, storing user preferences, and controlling portlet visibility relate more to application logic and backend functionalities rather than styling. Therefore, focusing on the role of CSS variables in defining reusable styling values is the key aspect of this question.