React bootstrap 4右侧导航下拉选项隐藏

Question

我正在使用react bootstrap v4。右侧导航下拉选项处于隐藏状态。我尝试了expanded={false}，但是没有运气。我已附上屏幕截图以供参考。请提出解决方案。

<Navbar collapseOnSelect expand="lg" bg="dark" variant="dark">
  <Navbar.Brand href="#home">React-Bootstrap</Navbar.Brand>
  <Navbar.Toggle aria-controls="responsive-navbar-nav" />
  <Navbar.Collapse id="responsive-navbar-nav">
    <Nav className="mr-auto">
      <Nav.Link href="#features">Features</Nav.Link>
    </Nav>
    <Nav>
      <NavDropdown title="Dropdown" id="collasible-nav-dropdown">
        <NavDropdown.Item href="#action/3.1">
          Awesome Action One
        </NavDropdown.Item>
      </NavDropdown>
    </Nav>
  </Navbar.Collapse>
</Navbar>