This appears to work on my Word 2016 and 365 machines
Code:
With Application.CommandBars("Navigation")
.Width = 300 ' set to whatever you want - the default seems wide at 400
.Visible = True
.Position = msoBarLeft
End With
'Application.TaskPanes(wdTaskPaneFormatting).Visible = True
With Application.CommandBars("Styles")
.Visible = True
.Position = msoBarRight
.Width = 600
End With