How do I format individual lines in a textbox via Microsoft PowerPoint macros?

I want a textbox where the first line and subsequent lines of text have different formatting, but they must be in the same textbox. This is what I currently have, which applies the same formatting to all text.

Sub geberateSlide() 
  ...
  With currSlide.Shapes.AddTextbox(Orientation:=msoTextOrientationHorizontal, _
  Left:=0, Top:=0, Width:=headerWidth, Height:=headerHeight)
    .TextFrame.TextRange.Text = "Test Box" & vbCrLf & "Description"
    .TextFrame.AutoSize = ppAutoSizeNone
    .Height = headerHeight
    .Line.ForeColor.RGB = RGB(0,0,0)
    .Line.Visible = True
  End With
...
End Sub

The text should be Arial 8. Line 1 should be black and bold, while subsequent text should be blue.

.TextFrame.TextRange.Lines(0, 1) will target the first line.

%300 Zoom

With currSlide.Shapes.AddTextbox(Orientation:=msoTextOrientationHorizontal, _
                                 Left:=0, Top:=0, Width:=headerWidth, Height:=headerHeight)
    .Height = headerHeight
    .TextFrame.AutoSize = ppAutoSizeNone
    With .TextFrame.TextRange
        .Text = "Test Box" & vbCrLf & "Description"
        With .Font
            .Color = vbBlue
            .Size = 8
            .Name = "Arial"
        End With

        With .Lines(1).Font
            .Color = vbBlack
            .Bold = msoTrue
        End With
    End With
End With