How to use the bs-css/src/Css.js.darkgray function in bs-css

/* [] */0
      ]
    ]);

var h2 = Css.style(/* :: */[
      Css.color(Css.red),
      /* [] */0
    ]);

var p = Css.style(/* :: */[
      Css.color(Css.black),
      /* [] */0
    ]);

var date = Css.style(/* :: */[
      Css.color(Css.darkgray),
      /* [] */0
    ]);

var Styles = /* module */[
  /* article */article,
  /* link */link,
  /* h2 */h2,
  /* p */p,
  /* date */date
];

function Post(Props) {
  var post = Props.post;
  return React.createElement("article", {
              className: article
            }, React.createElement(Gatsby.Link, {