def add_titlebox(ax, text, x=0.05, y=0.9, alignment='left', fontsize=12.5):
    """
    add title text box.
    
    Arguments:
        ax {`matplotlib.axes.Axes`} -- the `Axes` instance used for plotting.
        text {string} -- title text
    
    Keyword Arguments:
        x {float} -- title x position (default: {0.05})
        y {float} -- title y position (default: {0.9})
        alignment {str} -- horizontal alignment (default: {'left'})
        fontsize {float} -- text font size (default: {12.5})
    
    Returns:
        `matplotlib.axes.Axes` -- the `Axes` instance used for plotting.
    """

    ax.text(
        x, y, text, horizontalalignment=alignment, transform=ax.transAxes,
        bbox=dict(facecolor='white'), fontsize=fontsize)

    return ax