So for some reason even when I set window border to no border in window decorations, I still get a thin border on every window. This happens on Aritim, but not on plastik or breeze.

Here's a picture of the window border.
Here's what my settings look like.

Any help?

You do realize that Aritim is a third-party theme. You should ask the author of the theme, their website can be accessed from the System Settings