Centering mobile navigation menu button

app/views/templates/partials/header.twig

@@ -10,10 +10,12 @@
 <!-- nav bar -->
 <nav id="nav" class="navbar" class="row">
   <div class="container-fluid">
+    <div class="nav navbar-header">
       <button id="navbar-collapse-button" type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar-collapse" aria-expanded="false">
   	    <span class="sr-only">Toggle navigation</span>
   	    <i class="fa fa-bars" aria-hidden="true"></i>
   	  </button>
+    </div>
 
 	  <div class="collapse navbar-collapse" id="navbar-collapse">
 	    <ul class="nav navbar-nav">

assets/sass/partials/_navigation.sass

@@ -5,7 +5,8 @@
     display: inline-block
     float: none
 
-  .navbar-collapse
+  .navbar-collapse,
+  .navbar-header
     text-align: center
 
   ul