visitFontFace(node) {
    var buf = this.indent + '@font-face';
    buf += '\n';
    ++this.indents;
    for (var i = 0, len = node.declarations.length; i < len; ++i) {
      buf += this.visitDeclaration(node.declarations[i]);
    }
    --this.indents;
    return buf;
  }
Visit FontFace `node`.

@param {FontFace} node
@return {String}
@api private