code: def highlight_region(plt, start_x, end_x):
    
    start_x = convert_to_mdate(start_x)
    end_x = convert_to_mdate(end_x)
    plt.axvspan(start_x, end_x, color=CONSTANTS.HIGHLIGHT_COLOR, alpha=CONSTANTS.HIGHLIGHT_ALPHA)
docs: Highlight a region on the chart between the specified start and end x-co-ordinates.
    param pyplot plt: matplotlibk pyplot which contains the charts to be highlighted
    param string start_x : epoch time millis
    param string end_x : epoch time millis