How to center text in a rectangle?

Hi, could you please tell me :smiling_face_with_tear:
How can I center the text?
How can I make transparency without touching the transparency of the text? (The color becomes dull)
What we have now:

fig.add_vrect(x0=datetime.strptime('2022-01-01', '%Y-%m-%d').strftime('%d %b %Y'),
              x1=datetime.strptime('2022-01-7', '%Y-%m-%d').strftime('%d %b %Y'),
              y0=0.94, y1=1,
              annotation_position="top right",
              annotation_text="~4,57", annotation_align='center',
              fillcolor="green", opacity=0.25, line_width=0)