About Semantic UI
Volto uses Semantic UI and React Semantic UI as development framework. It helps you to create websites with responsive layouts using human-friendly HTML. Semantic UI treats words and classes as exchangeable concepts. Classes use syntax from natural languages like noun/modifier relationships, word order, and plurality to link concepts intuitively.
One of its main features is theming. Components in Semantic UI are designed to help developers adhere to progressive truthfulness in their development. Instead of having to create components from a blank canvas, developers using Semantic UI only need to specify how their components should differ from the default theme using CSS variables and other CSS overrides (if required).
It sports a sophisticated theming engine built with LESS CSS preprocessor that allows you to have different layers of defaults/CSS variables modifiers/CSS overrides in place, inheriting one from the parent in a sensible manner: