Using css/html dropdown as Mediawiki template

I am trying to use this dropdown as a Mediawiki template and allow for Mediawiki parameters in the URL creation (I.e. {{PAGENAME}}). Apparently, this type of html elements is not parsed. Trying $wgRawHtml = true; resulted in the template being displayed, but, apart from being a security risk, there was no way to have parsable elements. I did find this template but I could not figure out how do adapt it to work with the styling of the dropdown in question.

Solution

In the page MediaWiki:Common.css (or MediaWiki:Skinname.css, if you only want it for a certain skin), add your desired CSS:

 /* Dropdown Button */
.dropbtn {
  background-color: #4CAF50;
  color: white;
  padding: 16px;
  font-size: 16px;
  border: none;
}

/* The container <div> - needed to position the dropdown content */
.dropdown {
  position: relative;
  display: inline-block;
}

/* Dropdown Content (Hidden by Default) */
.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f1f1f1;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 1;
}

/* Links inside the dropdown */
.dropdown-content a {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
}
/* Change color of dropdown links on hover */
.dropdown-content a:hover {background-color: #ddd;}

/* Show the dropdown menu on hover */
.dropdown:hover .dropdown-content {display: block;}

/* Change the background color of the dropdown button when the dropdown content is shown */
.dropdown:hover .dropbtn {background-color: #3e8e41;}

If everything in the template is going to be an internal link, make this your template:

<div class="dropdown">
<div class="dropbtn">{{{title|Dropdown}}}</div>
<div class="dropdown-content"><!--
-->{{#if:{{{1|}}}|[[{{{1}}}]]}}<!--
-->{{#if:{{{2|}}}|[[{{{2}}}]]}}<!--
-->{{#if:{{{3|}}}|[[{{{3}}}]]}}<!--
-->{{#if:{{{4|}}}|[[{{{4}}}]]}}<!--
-->{{#if:{{{5|}}}|[[{{{5}}}]]}}<!--
</div>
</div>

And then invoke it like this:

{{dropdown|Foo|Bar|Baz}}

And it will make a dropdown with links to the pages Foo, Bar, and Baz on your wiki.

If you have to support external links or plaintext, use this instead:

<div class="dropdown">
<div class="dropbtn">{{{title|Dropdown}}}</div>
<div class="dropdown-content plainlinks"><!--
-->{{#if:{{{1|}}}|<span>{{{1}}}</span>}}<!--
-->{{#if:{{{2|}}}|<span>{{{2}}}</span>}}<!--
-->{{#if:{{{3|}}}|<span>{{{3}}}</span>}}<!--
-->{{#if:{{{4|}}}|<span>{{{4}}}</span>}}<!--
-->{{#if:{{{5|}}}|<span>{{{5}}}</span>}}<!--
--></div>
</div>

Change the as in the CSS to spans, and add a rule to make sure they are black instead of blue:

/* Links inside the dropdown */
.dropdown-content span {
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
}
/* Change color of dropdown links on hover */
.dropdown-content span:hover {background-color: #ddd;}

.dropdown-content a, .dropdown-content a:hover{
  color: black;
  text-decoration: none;
}

And then, you can invoke it like

{{dropdown|[[Foo]]|[https://www.google.com/ Google]|Plain text}}

and it has a link to the page Foo, a link to Google, and a plain-text menu item.

Note: If a parameter contains an equals sign (=), you need to specify all the parameter names, like this:

{{dropdown|1=[https://duckduckgo.com/?q=foo&ia=web Search for Foo]|2=Bar}}