Custom CSS properties, at-directives, pseudoClasses and pseudoElements https://github.com/microsoft/vscode-css-languageservice/blob/main/docs/customData.md

interface CSSDataV1 {
    atDirectives?: IAtDirectiveData[];
    properties?: IPropertyData[];
    pseudoClasses?: IPseudoClassData[];
    pseudoElements?: IPseudoElementData[];
    version: 1 | 1.1;
}

Properties

atDirectives?: IAtDirectiveData[]
properties?: IPropertyData[]
pseudoClasses?: IPseudoClassData[]
pseudoElements?: IPseudoElementData[]
version: 1 | 1.1