如何设置转置的MultiIndex DataFrame的样式

import pandas as pd

data = [['Alice', 'Math', 85],
        ['Alice', 'Science', 90],
        ['Bob', 'Math', 92],
        ['Bob', 'Science', 88]]

df = pd.DataFrame(data, columns=['Name', 'Subject', 'Score'])
df = df.set_index(['Name', 'Subject'])

                Score
Name  Subject        
Alice Math         85
      Science      90
Bob   Math         92
      Science      88

def set_style(value):
    # 设置样式的规则
    if value >= 90:
        return 'background-color: green'
    elif value >= 80:
        return 'background-color: yellow'
    else:
        return 'background-color: red'

styled_df = df.style.applymap(set_style)

styled_df.to_excel('styled_dataframe.xlsx', engine='openpyxl')