[]i want my button should be like that.but my button always stay in left1
I think the easiest way to do it is to just use a div! or you can create a custom component that does that for you.
<ListGroup.Item>
<div style={{ width: '100%', display: 'flex', justifyContent: 'center' }}>
<Button variant="primary">Primary</Button>
</div>
</ListGroup.Item>