The navigation menu button does not appear on small screens including in the browser reducing the screen.
You are using a child theme, as far as I can see. Most likely you are overriding the
header.php file that has changed a little bit with a recent theme update. So please make sure that this line:
<div class="btn-menu"><i class="sydney-svg-icon"><?php sydney_get_svg_icon( 'icon-menu', true ); ?></i></div>
…is between this line:
<div class="col-md-8 col-sm-4 col-xs-12">
…and this line:
<nav id="mainnav" class="mainnav" role="navigation">
Another thing I would like to know is how to reduce the space under the navigation menu to be able to add more content to the navigation bar.
I’m not sure what exactly you want to do, can you please provide more details and some explanatory screenshots?
Kind Regards, Roman.