Modifiers not applied on ChatMessage buttons

[pierrotsmnrd]

Software version info

• panel 1.3.8
• python 3.9.18

Description of expected behavior and the observed behavior

I'm using design modifiers to style a panel app (Ragna's UI).
I noticed that some modifiers were not applied to some widgets.
For instance, we have Button widgets in the UI, and some of them are inside ChatMessage objects.
The modifiers are applied for most of the buttons, except for the ones inside ChatMessage.

I don't know if this happens in other cases that ChatMessage.

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

import panel as pn

def index():

    standard_button = pn.widgets.Button(name="standard button")
    chat_message = pn.chat.ChatMessage(pn.widgets.Button(name="Button in chat message"))

    template = pn.template.FastListTemplate(title="bug with modifiers")
    template.main.append( pn.Column(standard_button, chat_message) )
    return template

pn.theme.fast.Fast.modifiers[pn.widgets.Button] = {
    "stylesheets": [" :host { background-color: red; }"]
}

pn.serve({"/":index})

Screenshots

This yields the following result, where we can see that only one button has a red background :

Looking at the generated code, we can see that the modifier is added to the first button, but not to the second :

• I may be interested in making a pull request to address this
  I have actually started digging inside Panel, but I need help understanding what's going on.