Remove Resize Bar

I am working at a little c# WPF program, to learn and try out c# and i want to enable resizing in my program, but i dont want that resize bar with borderless window.

So i tried already changing the thickness, stroke. But it didnt had any effect. After that i tried moving the content above the bar, but it comes out on top. After that i tried to make own resizing, which didnt worked. Now im back to the silly bar at the top.

Dont really have that much code, but what im using rn is:`


Here is a little screenshot: Also i wont use "CanResizeWithGrip", because this grip thing is stuck in my border and also it has the same bar.

I want to remove the black topbar on my program. Either overwriting it or smth else. Hope someone can help me :D