Menu disappears on small screens
According to this the problem, was that a div container pushed the menu away.

The old and wrong container was: 

&lt;div class="col-lg-12" id="content-container" style="
display: table-cell;"&gt;


It could be fixed by adding additional bootstrap classes:

&lt;div class="col-xs-12 col-sm-12 col-md-12 col-lg-12" id="content-container"&gt;