Code:
dialog test {
  title "Test Dialog"
  size [color:blue]$calc($window(-1).w - 100)[/color] 0 [color:red]100[/color] 100
}


The blue test is calculating the X position by subtracting the width of the dialog from the width of the resolution ($window(-1).w). The dialog should appear in the top right corner.

Code:
dialog test2 {
  title "Test Dialog (2)"
  size $calc($window(-1).w - 100) [color:green]$calc($window(-1).h - 100)[/color] 100 [color:orange]100[/color]
}


This dialog will open in the bottom right corner. The green text is used in this case to subtract the height of the dialog from the height of the resolution ($window(-1).h).