With the latest planned upgrade to the Bootstrap web development framework, builders are offering CSS variables for all components, along with new helpers and utilities. Bootstrap v5.2.0-beta1 ...

CSS is the standard and preferred mechanism for formatting HTML pages. Conforming with the separation of concerns design pattern and best practice, cascading style ... Making it possible to customize ...

Such frameworks do not enforce using JavaScript to style components, but they lend themselves to it. Consequently, a number of CSS-in-JS libraries have come forward to make the process easier.