NavBar - Which property to add class to navbar-header?

I’ve included the default Yii2 output below for reference. I’m wanting to add a class to the div that gets “navbar-header” but for all my attempts I haven’t been able to identify the property to apply it on. Any tips?

<nav id="w0" class="navbar-inverse navbar-fixed-top navbar" role="navigation">

  <div class="container">

    <div class="navbar-header">

      <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#w0-collapse">

        <span class="sr-only">Toggle navigation</span>

        <span class="icon-bar"></span>

        <span class="icon-bar"></span>

        <span class="icon-bar"></span>


      <a class="navbar-brand" href="/">My Company</a>


    <div id="w0-collapse" class="collapse navbar-collapse">

      <ul id="w1" class="navbar-nav navbar-right nav">

        <li class="active"><a href="/site/index.html">Home</a></li>

        <li><a href="/site/about.html">About</a></li>

        <li><a href="/site/contact.html">Contact</a></li>

        <li><a href="/site/signup.html">Signup</a></li>

        <li><a href="/site/login.html">Login</a></li>





Thanks in advance,

Pedro :)