After spending a week trying to make my beautiful CSS menu responsive and add drop down sub-menus with unlimited depth, I've hit a roadblock. I can't seem to figure out how to achieve both functionalities simultaneously. Is there anyone out there who can help me navigate through this challenge and make my menu responsive and dropdown?
HTML
<header id="header" class="page-header js-header" data-selenium="page-header">
<div class="main-nav">
<div class="nav" id="main_menu">
<ul class="topnav">
<li><a href="/c/browse/Photography/ci/989/N/4294538916" target="_self"><span>Photography</span></a></li>
<li><a href="/c/browse/Computers-Solutions/ci/9581/N/4294542559 " target="_self"><span>Computers</span></a></li>
<li><a href="/c/browse/Professional-Video/ci/3755/N/4294545851" target="_self"><span>Pro Video</span></a></li>
<li><a href="/c/browse/Lighting-Studio/ci/1161/N/4294551176" target="_self"><span>Lighting <span class="lighting">& Studio</span></span></a>
<ul class="hidden">
<li><a href="#">Drop Down Test</a></li>
<li><a href="#">Drop Down Test</a></li>
<li><a href="#">Drop Down Test</a></li>
</ul>
</li>
<li><a href="/c/browse/Professional-Audio/ci/12154/N/4294550705" target="_self"><span>Pro Audio</span></a></li>
<li><a href="/c/browse/Mobile/ci/8565/N/4294542748" target="_self"><span>Mobile</span></a></li>
<li><a href="/c/browse/Home-Entertainment/ci/4600/N/4294544179" target="_self"><span>TVs & Entertainment</span></a></li>
<li><a href="/c/browse/Camcorders/ci/1820/N/4294548420" target="_self"><span>Camcorders</span></a></li>
<li><a href="/c/browse/Surveillance-Video/ci/3496/N/4293342959" target="_self"><span>Surveillance</span></a>
<ul>
<li><a href="#">Drop Down Test</a></li>
<li><a href="#">Drop Down Test</a></li>
<li><a href="#">Drop Down Test</a></li>
</ul>
</li>
<li><a href="/c/browse/Binoculars-Scopes/ci/978/N/4294541872" target="_self"><span>Optics</span></a></li>
<li><a href="/c/browse/A-V-Presentation/ci/3644/N/4294546288" target="_self"><span>A/V Presentation</span></a></li>
<li class="border-link"><a href="/c/category/2870/Used_Equipment.html">Used</a></li>
<li class="border-link"><a href="/explora">Boogers</a></li>
<li class="icon">
<a href="javascript:void(0);" onclick="myFunction()">☰</a>
</li>
</ul>
</div>
</div>
</header>
CSS
(CSS code here...
If you'd like to experiment with the code, here's the link to the fiddle: https://jsfiddle.net/zyh7grur/1/