Hard relation to custom.css will lead to 404 when using different theme

[hille721]

The hard inclusion of custom.css (

sphinx-argparse-cli/src/sphinx_argparse_cli/__init__.py

Line 9 in 4a542ff

app.add_css_file("custom.css")

) will lead to a 404 error when using different themes (e.g. sphinx_rtd_theme or sphinx_immaterial):

[gaborbernat]

We should remove that 👍 PR welcome.