Description
Pandas version checks
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I have checked that this issue has not already been reported.
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
df = pd.DataFrame({"a": [1]})
styler = df.style.applymap(lambda x: "border-style: hair; border-color: black")
styler.to_excel(r"test_border.xlsx", engine="xlsxwriter")Issue Description
The CSSToExcelConverter._border_style function does not return any value (i.e., None) when the style string is not recognized. However, "hair" should be a recognized style string in xlsxwriter, corresponding to border index "7". This leads to a crash in xlsxwriter. Moreover, there is no path to actually return the "hair" style for any engine.
Expected Behavior
Use of border-style: hair will export a spreadsheet with the correct formatting.
Installed Versions
INSTALLED VERSIONS
commit : 224458e
python : 3.10.4.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19044
machine : AMD64
processor : Intel64 Family 6 Model 142 Stepping 12, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United States.1252
pandas : 1.5.0rc0
numpy : 1.21.6
pytz : 2022.1
dateutil : 2.8.2
setuptools : 63.4.1
pip : 22.1.2
Cython : None
pytest : 7.1.2
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : 3.0.3
lxml.etree : 4.9.1
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.4.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : 1.3.5
brotli : None
fastparquet : 0.5.0
fsspec : None
gcsfs : None
matplotlib : None
numba : 0.55.2
numexpr : 2.8.3
odfpy : None
openpyxl : 3.0.10
pandas_gbq : None
pyarrow : 8.0.0
pyreadstat : 1.1.9
pyxlsb : None
s3fs : None
scipy : None
snappy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : 2.0.1
xlwt : None
zstandard : None
tzdata : None