"Keyword Arguments" section created by numpydoc looks poor with default theme when there's a single kwarg.

Describe the bug

The default theme should probably arrange for the "Keyword Arguments" section header created by numpydoc to fit in a single line, as splitting it in two lines can result in awkward layouts.

How to Reproduce

In a clean directory

$ cat >project.py <<EOF
def foo(*, kwarg):
    """
    Foos it.

    Keyword Arguments
    -----------------
    kwarg : int
        It's the kwarg.
    """
EOF
sphinx-apidoc . -o . -F -A me -V 0.0 --extensions sphinx.ext.napoleon
PYTHONPATH=. make html

Expected behavior

The "Keyword Arguments" header should not be longer (in lines) than the actual contents of the section.

Your project

N/A, see script above to generate it.

Screenshots

OS

linux

Python version

3.10

Sphinx version

4.3.2

Sphinx extensions

sphinx.ext.napoleon

Extra tools

N/A

Additional context

No response

Start by reproducing the layout in a clean directory with the provided project.py, sphinx-apidoc command, and make html using the default theme. Inspect the generated HTML and theme styling to identify why a single keyword argument causes the header to wrap. Done means the "Keyword Arguments" header fits in no more lines than the section contents without breaking other generated documentation layouts.