TextBox border color accent color.

[viniciusjarina]

TextBox border color seems to not being updated properly.

This seem related to LinearGradientBrushes.

It seems when UpdateBrush only update SolidColorBrushes.

Maybe we can change the logic to check for LinearGradientBrush and change the stops colors.

Btw: Congratulations this project is really good. I love it.