The CSS.registerProperty() static method registers custom properties, allowing for property type checking, default values, and properties that do or do not inherit their value.| MDN Web Docs
Cascading Style Sheets (CSS) is a stylesheet language used to describe the presentation of a document written in HTML or XML (including XML dialects such as SVG, MathML or XHTML). CSS describes how elements should be rendered on screen, on paper, in speech, or on other media.| MDN Web Docs
1. Introduction| drafts.css-houdini.org