WpfMessageBox | WPF message box , with optional features like custom buttons

I have a custom message box with two button 'Yes' and 'No'. Button 'Yes' is green and button 'No' is red.

I apply the same style for the two buttons through a xaml file defined separately as below:

MsgBoxButtonStyle.xaml:

I've created a custom error box with a rectangle for a header bar (the window is borderless). I'm trying to get the header rectangle to work like any window header bar and allow dragging to move. I have the code in place, however it only works by the edge of the rectangle (approx half a cm) and not anywhere in the rectangle.

I've set the height, width, and fill of the rectangle but not sure if there's a property I'm missing somewhere which allows click drag to work anywhere?

Rectangle definition:

I'm creating a custom error box which allows me to store additional information (and other features which aren't relevant). The textbox should be able to scroll to adapt to error messages. However, I believe there is an issue with the height. The contents of the expander go beyond the max height of the window. As a result, the scrollbar is considered not required even though it is off the screen.

How can I get the scrollbar to work as expected?

Error Window:

XML Definition:

I have a custom messagebox done in wpf.

Custom messagebox view xaml:

I have converted the following C# code to VB.NET code via http://converter.telerik.com/