CSS variables are here for ages
Every front-end developer that starts reading about CSS preprocessors thinks “Oh, finally variables in CSS". Indeed, the ability to create and use variables in CSS makes our code much more flexible. However, I think that there is no need to use a preprocessor to create flexible stylesheets.
Presentational and container React components
When we start using React we very soon also start asking questions. Where I’m suppose to put my data, how to communicate changes or how to manage state? The answers of this questions are very often matter of context and sometimes just practice and experience with the library. However, there is a pattern which is used widely and helps organizing React based applications - splitting the components into presentational and containers.