Date Picker not overflowing the sidebar

[totla-deshaw]

ALL software version info

(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc should be added within the dropdown below.)

Software Version Info

```plaintext Panel 1.4.5 ```

Description of expected behavior and the observed behavior

Hi team,

The datepicker does not seem to overflow the sidebar like the other widgets. Feels like a bug but is there any quick CSS fix for this?

Complete, minimal, self-contained example code that reproduces the issue

import panel as pn
from deshaw.djs.panel import DJSTemplate
from datetime import datetime

app = pn.template.FastListTemplate()

datewidget1 = pn.widgets.DatePicker(
    name='Datetime Picker', value=datetime(2021, 3, 2), width=200
)
datewidget2 = pn.widgets.DatePicker(
    name='Datetime Picker', value=datetime(2021, 3, 2), width=200
)

selectwidget = select = pn.widgets.Select(name='Select', options=['Biology', 'Chemistry', 'Physics'], width=600)

app.sidebar.append(pn.Row(datewidget1, datewidget2))
app.sidebar.append(selectwidget)
app.main.append("# asasd")

app.servable()

Stack traceback and/or browser JavaScript console output

No errors

Screenshots or screencasts of the bug in action

• [ ] I may be interested in making a pull request to address this

[ahuang11]

Potentially modifying the stylesheet of the DatePicker calendar's zIndex, similar to https://github.com/holoviz/holoviews/pull/6297