anchorSpecifier
An optional anchor specifier, as defined in https://www.w3.org/TR/css-anchor-position-1/#anchor-specifier. If not provided, it will return the implicit anchor element for the given positioned element.
An optional anchor specifier, as defined in https://www.w3.org/TR/css-anchor-position-1/#anchor-specifier. If not provided, it will return the implicit anchor element for the given positioned element.