Fix --preview-window noborder with non-default background color

src/tui/tui.go

@@ -221,6 +221,8 @@ type BorderStyle struct {
 	bottomRight rune
 }
 
+type BorderCharacter int
+
 func MakeBorderStyle(shape BorderShape, unicode bool) BorderStyle {
 	if unicode {
 		return BorderStyle{
@@ -244,6 +246,17 @@ func MakeBorderStyle(shape BorderShape, unicode bool) BorderStyle {
 	}
 }
 
+func MakeTransparentBorder() BorderStyle {
+	return BorderStyle{
+		shape:       BorderAround,
+		horizontal:  ' ',
+		vertical:    ' ',
+		topLeft:     ' ',
+		topRight:    ' ',
+		bottomLeft:  ' ',
+		bottomRight: ' '}
+}
+
 type Renderer interface {
 	Init()
 	Pause(clear bool)