Not proper bootstrap navbar in laravel project

I'm struggling with my laravel project (5.5) to use a bootstrap navbar from the starter template.

I'm trying to use an include of the navbar partial, or just directly put the code of the navbar in the blade template, but here's how it's displayed

(I tried on 2 different projects, I get the same thing) :

And here's the original version :

Here's the code that i use :

< nav class="navbar navbar-inverse navbar-fixed-top">
    <div class="container">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar" aria-expanded="false" aria-controls="navbar">
                <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="#">Project name</a>
        </div>
        <div id="navbar" class="collapse navbar-collapse">
            <ul class="nav navbar-nav">
                <li class="active"><a href="#">Home</a></li>
                <li><a href="#about">About</a></li>
                <li><a href="#contact">Contact</a></li>
            </ul>
        </div><!--/.nav-collapse -->
    </div>
</nav>

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