def _add_ref_line(plot, ref_time, ref_text='Ref time', series_count=1):
    'Add a reference marker line and label at `ref_time`.'
    ref_label_tm = pd.Timestamp(ref_time)
    plot.line(x=[ref_label_tm, ref_label_tm], y=[0, series_count])
    ref_label = Label(x=ref_label_tm, y=0, y_offset=10, x_units='data', y_units='data', text=f'< {ref_text}', text_font_size='8pt', render_mode='css', border_line_color='red', border_line_alpha=1.0, background_fill_color='white', background_fill_alpha=0.5)
    plot.add_layout(ref_label)
Add a reference marker line and label at `ref_time`.
def _add_ref_line(plot, ref_time, ref_text='Ref time', series_count=1):
    
    ref_label_tm = pd.Timestamp(ref_time)
    plot.line(x=[ref_label_tm, ref_label_tm], y=[0, series_count])
    ref_label = Label(x=ref_label_tm, y=0, y_offset=10, x_units='data', y_units='data', text=f'< {ref_text}', text_font_size='8pt', render_mode='css', border_line_color='red', border_line_alpha=1.0, background_fill_color='white', background_fill_alpha=0.5)
    plot.add_layout(ref_label)