public virtual string NavFill(NavFillType fillType) => fillType == NavFillType.Justified ? "nav-justified" : "nav-fill";
public string NavFill(NavFillType fillType) => null;
public override string NavFill(NavFillType fillType) => fillType == NavFillType.Justified ? "nav-justified" : "nav-fill";
public abstract string NavFill(NavFillType fillType);