onClick toggle the next sibling of an element

toggle-next-sibling.js

function gravdept_next(elem) {
    do {
        elem = elem.nextSibling;
    } while (elem && elem.nodeType != 1);
    return elem;                
}

function gravdept_toggle(elem) {
    var nextElem = gravdept_next(elem);
	
    if (nextElem.style.display==='block') { nextElem.style.display='none'; }
    else { nextElem.style.display='block'; }
}

/**
 * Example markup:
 *
 * <a href="#" onclick="gravdept_toggle(this); return false;">Toggle It</a>
 * <div>Something to show/hide</div>
 *
 */

With the help of StackOverflow of course:
http://stackoverflow.com/questions/868407/hide-an-elements-next-sibling-with-javascript

If you want it to work the first time you click using the example above, you need to reverse the if statement in the second function

function gravdept_toggle(elem) {
    var nextElem = gravdept_next(elem);
	
    if (nextElem.style.display==='none') { nextElem.style.display='block'; }
    else { nextElem.style.display='none'; }
}

Working Example: https://codepen.io/Realto619/pen/wvrJZzb