def background_negative_green(val):
    """
    Changes the background color of a cell in DataFrame according to its value.

    Parameters
    ----------
    val : float
        single cell value in a pandas DataFrame.

    Returns
    -------
    str
        return background color for the cell of pandas DataFrame.

    """
    if val == "":
        color = "white"
    elif val < -200:
        color = "#009900"
    elif -200 <= val < -150:
        color = "#00cc00"
    elif -150 <= val < -100:
        color = "#80ff80"
    elif -100 <= val < -50:
        color = "#b3ffb3"
    elif -50 <= val < 0:
        color = "#e6ffe6"
    else:
        color = "white"

    return f"background-color: {color}"