small fix to make dialog buttons white when dark theme is enabled

Django Admin dark mode support (#9)

* Better Django Admin dark mode support

Removes                 
```.flex-container:has(trix-editor) {
    display: block;
}```
and adds `div` that wraps `<trix-editor />` tag so TrixEditorWidget could display correctly in Django Admin's field with `.flex-container` class.

Also adds dark mode styles for Trix in Django Admin.

* Update setup.py - version='0.4'

updated with permission decorator