Disable the blue border of not-maximized windows

[ralf3u]

I installed Kvantum and chosed Arc-Dark. But there is a blue border around not-maximized windows that I don’t like, because it is too intense.

Is there a possibility to disable the blue border around not-maximized windows or rather to change the color?
Thank you for an answer in advance.

Here is an example:

[That_Random_Guy]

I recall having to change either the theme or something in the appearance settings somewhere.

I think it was Openbox last time I had to change it. Please see the following and try changing the themes:
https://manual.lubuntu.me/stable/3/3.2/3.2.11/openbox_settings.html

[ralf3u]

@That_Random_Guy

Yes, indeed. I changed in Openbox in “Theme” from “Lubuntu Arc” to “KvSimplicityDark” (other theme that I like is “KvGnomeDark” because the window menu is dark). And now there is no blue border any more.

Thank you so much for your help.