Smooth the edges of AG Mini settings window to look more like a native macOS app

[windwak3r]

Issue Details

At the moment, the edges of the settings window appear sharp.

Proposed solution

The edges need to be made smoother, in line with the style of modern macOS.

Alternative solution

No response

[windwak3r]

@JohnnyFireOne Issue with edges gonna be here.

[JohnnyFireOne]

@windwak3r

still remains the same with new ver 2.1.0