style property of FloatContainer does not apply to the text in CompletetionsMenu

Adding a style attribute to change the color of the text given in a CompletionsMenu embedded in the floats list of a FloatContainer does not work.

This issue can be reproduced by adding style="red italic bold" to the following sample, as shown below:
python-prompt-toolkit/examples/full-screen/simple-demos/autocompletion.py:

body = FloatContainer(
    content=HSplit(
        [
            Window(
                FormattedTextControl('Press "q" to quit.'), height=1, style="reverse"
            ),
            Window(BufferControl(buffer=buff)),
        ]
    ),
    floats=[
        Float(
            xcursor=True,
            ycursor=True,
            content=CompletionsMenu(max_height=16, scroll_offset=1),
        ),
    ],
    style="red italic bold"
)

Output:

You can see that text in the completions menu is bold and italic, but not red. So, while all other styles are picked by the completions menu but not the text color.

Start with python-prompt-toolkit/examples/full-screen/simple-demos/autocompletion.py and reproduce the issue by adding style="red italic bold" to the FloatContainer. Trace how FloatContainer and CompletionsMenu apply styles, then verify that the completions text also receives the color while retaining the bold and italic styles.