BUG: Multiple CSS selectors using set_table_styles and dict form of table_styles
### 

- [X] I have checked that this issue has not already been reported.

- [X] I have confirmed this bug exists on the [latest version](https://pandas.pydata.org/docs/whatsnew/index.html) of pandas.

- [x] I have confirmed this bug exists on the master branch of pandas.


### Reproducible Example

```python
import pandas as pd
df = pd.DataFrame([range(5) for _ in range(5)], columns=list('abcde'))
styled = df.style.set_table_styles({
    'b': [{'selector': 'th, td', 'props': [('border-left', '2px solid black')]}]
})
# styled = df.style.set_table_styles({
#     'b': [{'selector': 'th', 'props': [('border-left', '2px solid black')]},
#           {'selector': 'td', 'props': [('border-left', '2px solid black')]}]
# })
html = styled.render()
with open('css_style_bug.html', 'w') as f:
    f.write(html)
```


### Issue Description

This is a minor issue when styling a table for html display. When setting a table style for a specified column using `set_table_styles`, the column is only applied to the final selector tag if they are named in a comma seperated list.

This seems to be similar to issue #34061.

### Expected Behavior

I have commented out, in the above examples, a workaround which does the expected behaviour.

### Installed Versions

<details>


INSTALLED VERSIONS
------------------
commit           : 73c68257545b5f8530b7044f56647bd2db92e2ba
python           : 3.8.10.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.4.72-microsoft-standard-WSL2
Version          : #1 SMP Wed Oct 28 23:40:43 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : C.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.3.3
numpy            : 1.21.2
pytz             : 2021.3
dateutil         : 2.8.2
pip              : 20.0.2
setuptools       : 44.0.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 3.0.2
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
