CSS custom properties don't work in media queries. Custom media queries could help out here but unfortunately, they're not supported yet.
Topic: CSS – Page 6
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.
A SVG/CSS trick to apply natural looking shadows to DOM elements.