navbar dropdown menus display issue on mobile and small devices with media query

问题

Not a big expert in CSS and responsiveness design, I try to collapse my navbar using a media query. The issue is that for dropdown menus, the responsive design is not applied correctl : The dropdown menus are displayed like on a large desktop device.

What I want is this :

Result Expected

But the result I obtain is this :

Current result

My code is actually the following :

    <nav class="navbar navbar-default">
        <div class="container-fluid">
            <!-- Brand and toggle get grouped for better mobile display -->
            <div class="navbar-header">
                <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1"> <span class="sr-only">Toggle navigation</span>
     <span class="icon-bar"></span>
     <span class="icon-bar"></span>
     <span class="icon-bar"></span>
    </button> <a class="navbar-brand" href="#">Brand</a>

            </div>
            <!-- Collect the nav links, forms, and other content for toggling -->
            <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
                <ul class="nav navbar-nav">
                    <li class="active"><a href="#">Link <span class="sr-only">(current)</span></a>

                    </li>
                    <li><a href="#">Link</a>

                    </li>
                    <li class="dropdown"> <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Dropdown <span class="caret"></span></a>

                        <ul class="dropdown-menu" role="menu">
                            <li><a href="#">Action</a>

                            </li>
                            <li><a href="#">Another action</a>

                            </li>
                            <li><a href="#">Something else here</a>

                            </li>
                            <li class="divider"></li>
                            <li><a href="#">Separated link</a>

                            </li>
                            <li class="divider"></li>
                            <li><a href="#">One more separated link</a>

                            </li>
                        </ul>
                    </li>
                </ul>
                <form class="navbar-form navbar-left" role="search">
                    <div class="form-group">
                        <input type="text" class="form-control" placeholder="Search">
                    </div>
                    <button type="submit" class="btn btn-default">Submit</button>
                </form>
                <ul class="nav navbar-nav navbar-right">
                    <li><a href="#">Link</a>

                    </li>
                    <li class="dropdown"> <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Dropdown <span class="caret"></span></a>

                        <ul class="dropdown-menu" role="menu">
                            <li><a href="#">Action</a>

                            </li>
                            <li><a href="#">Another action</a>

                            </li>
                            <li><a href="#">Something else here</a>

                            </li>
 <li class="divider"></li>
                        <li><a href="#">Separated link</a>

                        </li>
                    </ul>
                </li>
            </ul>
        </div>
        <!-- /.navbar-collapse -->
    </div>
    <!-- /.container-fluid -->
</nav>

And my media query is the current one as I found googling the web :

@media (max-width: 992px) {
    .navbar-header {
        float: none;
    }
    .navbar-left,.navbar-right {
        float: none !important;
    }
    .navbar-toggle {
        display: block;
    }
    .navbar-collapse {
        border-top: 1px solid transparent;
        box-shadow: inset 0 1px 0 rgba(255,255,255,0.1);
    }
    .navbar-fixed-top {
        top: 0;
        border-width: 0 0 1px;
    }
    .navbar-collapse.collapse {
        display: none!important;
    }
    .navbar-nav {
        float: none!important;
        margin-top: 7.5px;
    }
    .navbar-nav>li {
        float: none;
    }
    .navbar-nav>li>a {
        padding-top: 10px;
        padding-bottom: 10px;
    }
    .collapse.in{
        display:block !important;
    }
}

Additional info : The menu is displayed well when the viewport size is under 768px.

I guess, there is something missing on my media query for handling the dropdown menu case but I don't know what it is ? Can somebody help me ?

Thanks a lot.