toggle button not working in asp net core (Mobile View in browser).

here is my _Layout.cshtml file. What i am doing wrong? Please Help!

<environment exclude="Development">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css"
          integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh"
          crossorigin="anonymous">
    asp-fallback-href="~/css/bootstrap.min.css"
    asp-fallback-test-class="sr-only"
    asp-fallback-test-property="position"
    asp-fallback-test-value="absolute"
    asp-suppress-fallback-integrity="true"
   </environment>

<link href="~/css/site.css" rel="stylesheet" />


<title>@ViewBag.Title</title>
<div class="container">
    <nav class="navbar navbar-expand-sm bg-dark navbar-dark">
        <a class="navbar-brand" asp-controller="Home" asp-action="Index">
            <img src="~/images/employees.jpg" height="30" width="30" />
        </a>
        
        <button class ="navbar-toggler" type="button" data-toggle="collapse" 
                data-target="#collapsibleNavbar">
            <span class="navbar-toggler-icon"></span>
        </button>

        <div class="collapse navbar-collapse" id="collapsibleNavbar">
            <ul class="navbar-nav">
                <li class="nav-item">
                   <a class="nav-link" asp-controller="Home" asp-action="Index">List</a>
                </li>
            
                <li class="nav-item">
                   <a class="nav-link" asp-controller="Home" asp-action="Create">Create</a>
                </li>
            </ul>
        </div>
        </nav>
        
    <div>
        @RenderBody()
    </div>


    @if (IsSectionDefined("Scripts"))
    {
        @RenderSection("Scripts", required: true)
    }
</div>
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