create(obj) {
    const sheet = new Sheet(obj);
    // todo: add options param to allow create dynamic stylesheets that should not be stored
    this.sheets.push(sheet);
    if (this.builded) {
      sheet.calc(this.globalVars);
    }
    return sheet.getResult();
  }
Creates stylesheet that will be calculated after build
@param {Object} obj
@returns {Object}