The CSS Color Module Level 4 spec made rgba() and hsla() legacy CSS color functions. They're now aliases for rgb() and hsl().
Topic: CSS – Page 5
CSS custom properties don't work in media queries. Custom media queries could help out here but unfortunately, they're not supported yet.
Media queries can have a boolean context even though they allow more than two values.
A wild syntax to detect if a browser support a given media query.
Ways to hyphenate words and how the document language affects automatic hyphenation.