Semantic UI is a modern front-end development framework, powered by LESS and jQuery. It has a sleek, subtle, and flat design look that provides a lightweight user experience. Instead of creating components from a blank background, semantic UI can be used to specify how components should differ from the default theme using CSS variables.
Highlighting features is that it comes prebuilt with 50+ UI elements and 3000 + CSS variables
The framework uses em and rem units for its elements, making it fully responsive and adaptive to any size. You need only to change the base font and all other elements will adjust accordingly.