Bootstrap Navbar没有响应并且无法正常切换

Question

试图使该导航栏响应，所以我放置了navbar-expand-lg，但现在它始终从768px扩展。希望有人可以帮助我。

<nav class="navbar bg-light navbar-light fixed-top navbar-expand-lg">


        <a class="navbar-brand" href="index.html"><img style="max-width: 240px; max-height: 50px;" src="img/logo.png"></a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
            <span class="navbar-toggler-icon"></span>
        </button>

        <div class="collapse navbar-collapse" id="navbarNav">
            <ul class="navbar-nav mx-auto center-block align">
                <li class="nav-item nav-link nav-link-ltr">
                    <a class="nav-link scroll-link" href="#top-content">Page1</a>
                </li>
                <li class="nav-item nav-link nav-link-ltr">
                    <a class="nav-link scroll-link" href="#section-1">Page2</a>
                </li>
                <li class="nav-item nav-link nav-link-ltr">
                    <a class="nav-link scroll-link" href="#section-2">Page3</a>
                </li>
                <li class="nav-item nav-link nav-link-ltr">
                    <a class="nav-link scroll-link" href="#section-3">Page4</a>
                </li>
                <li class="nav-item nav-link">
                    <a style="border-radius: 25px;
                    color: rgba(255,255,255,1);
                    background-image: linear-gradient(to right, #3ea948 0%, #1d7235 51%, #0e4c25 100%);" class="nav-link scroll-link" href="#section-4">Page5</a>
                </li>

            </ul>
            <ul class="nav navbar-nav navbar-right">
         <li><a href="https://www.instagram.com"><img style="width: 47px; height: 47px;" src="img/insta.png"> </a></li>
         <li><a href="https://www.facebook.com"><img style="width: 47px; height: 47px;" src="img/face.png"> </a></li>

       </ul> 
        </div>

</nav>