Flex UI is a neat CSS framework based on BEC method and CSS3 flexbox model.
Unlike the complex CSS methodologies, BEC is Simplified and designer-centric CSS method. It is designed for cross-team communication.
Base: Branding and every fundamental elements that could affect the whole design look and feel.
Element: In view of the uniqueness of elements, we need a category specified for HTML elements and components.
Common: Elements that also affect globally but less important than Base. Third-party libraries or helpers also belong to this category.