arc-kde dark changes the background color of Libreoffice icons which makes many of the icons very difficult to see because they have dark insignia on a dark background.
Even though Libreoffice claims it can use Firefox Persona themes, that feature does not work, so there is no way (that I can find) to change it back.
From what I have read Libreoffice pulls its theme from the default system settings.
In my system LO is installed at /usr/lib/libreoffice/
Here is a screenshot of what I am talking about:
