Potential issue in Styler.to_excel() with Styler.set_properties()
#### Code Sample, a copy-pastable example if possible

    df = pd.DataFrame((np.random.rand(5, 4)*100), columns=list('ABCD'))
    df_style = df.style.set_properties(**{'background-color': 'black',
                                           'color': 'lawngreen',
                                           'border-color': 'white'})
    display(df_style)
    df_style.to_excel('test.xlsx')

#### Problem description

I was using the Styler.set_properties() function to format the Pandas Dataframe, while it (df_style) shows up nicely in Jupyter Notebook, it caused an error in the Styler.to_excel() function. Could you please advise how I can fix it?

[Issue also posted in stackoverflow.com: https://stackoverflow.com/questions/59161827/error-in-pandas-styler-set-properties-with-styler-to-excel]

#### Expected Output
Error in Styler.to_excel():

TypeError: tuple indices must be integers or slices, not dict

#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.15.0-1054-aws
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : C.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.25.3
numpy            : 1.17.3
pytz             : 2019.3
dateutil         : 2.8.0
pip              : 19.3.1
setuptools       : 42.0.1.post20191125
Cython           : 0.29.14
pytest           : 5.3.0
hypothesis       : None
sphinx           : 2.2.1
blosc            : None
feather          : None
xlsxwriter       : 1.2.6
lxml.etree       : 4.4.1
html5lib         : 1.0.1
pymysql          : None
psycopg2         : 2.8.4 (dt dec pq3 ext lo64)
jinja2           : 2.10.3
IPython          : 7.9.0
pandas_datareader: None
bs4              : 4.8.1
bottleneck       : 1.3.1
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.4.1
matplotlib       : 3.1.1
numexpr          : 2.7.0
odfpy            : None
openpyxl         : 3.0.1
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.3.1
sqlalchemy       : 1.3.11
tables           : 3.6.1
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.6
</details>
