Open a new window functionality misses CSS styling of a new window in React 17

[LukaszW007]

I use open-in new window option (https://ticlo.github.io/rc-dock/examples/#panel-extra or https://ticlo.github.io/rc-dock/examples/#panel-extra). I noticed that when I add new components to this opened, new window, they don't have applied CSS styling.
I use:

• React 17
• rc-dock 3.2.10

To reproduce:
I have an app based on rc-dock with an option to open a window in a new browser's window (rc-dock functionality). I also have a button to add a new react component (text area) with styling to this already-opened window.
When I use that button to add a text area to a window that is not opened in another browser's window, then everything works fine. I mean here, that the added text area has applied style.
In a case, when I first 'open in a new window' and then add a text area, then the text area is missing styling. In DOM a text area element has an attribute class with the correct class name eg. class="className" but none of CSS properties are applied (in DevTools's Styles tab this text area doesn't have any properties even though there is a div with className in DOM)

In the screenshot below, to the left text area with styling in the main browser's window, and on the right-hand side a window opened in a new browser's window (rc-dock open in a new window)