SideNav button

Hi!

SideNav button disappears in full screen mode, and appears only in window mode.

How to fix this problem, and make SideNav button continuously visible, independent from screen mode?

<!--Double Navigation -->
<header>

    <!-- Sidebar navigation -->
    <div id="slide-out" class="side-nav sn-bg-1">  <!--"fixed" sn-bg-1  removed! wide red darken-4-->   
      <ul class="custom-scrollbar">

      </ul>

  <!--div class="sidenav-bg red darken-4"></div-->
</div> <!--/. Sidebar navigation     -->

<!--Navbar -->
  <nav class="navbar fixed-top navbar-toggleable-md navbar-expand-lg navbar-dark red darken-4 scrolling-navbar double-nav"> <!--  primary-color -->

    <!-- SideNav slide-out button float-left -->
    <div class="float-left">
      <a href="#" data-activates="slide-out" class="button red darken-4 p-3 button-collapse black-text">
        <i class="fas fa-bars"></i>
      </a>
    </div>
</nav> <!--/.Navbar-->

Expected behavior (just in window mode)

Actual behavior (in full screen mode)

Resources (screenshots, code snippets etc.)