Update dropdown shortcode to use HTML details

Karl

15.27.2020 d0f9ca61a9fb7e4c6633127fddf797a2699e0140

 layouts/partials/head.html

@@ -45,14 +45,6 @@
</noscript>

<script>
    function toggleDisplay( elementID ) {
        elem = document.getElementById(elementID);
        if( elem.style.display == "none" ) {
            elem.style.display = "block";
        } else if( elem.style.display == "block" ) {
            elem.style.display = "none";
        }
    }
    {{ with .Site.Params.images }}
    function randomHeaderImg() {
        let images = [