CSSVariableReferenceValue
open class CSSVariableReferenceValue(var variable: String, val fallback: CSSUnparsedValue? = definedExternally)(source)
The CSSVariableReferenceValue interface of the CSS Typed Object Model API allows you to create a custom name for a built-in CSS value. This object functionality is sometimes called a "CSS variable" and serves the same purpose as the var() function. The custom name must begin with two dashes.