Basic Content/Menu Accordion

accordion.js

/* =====================================
Accordion
======================================== */
var accItem = document.getElementsByClassName('accordionItem');
var accHD = document.getElementsByClassName('accordionItemHeading');
for (i = 0; i < accHD.length; i++) {
    accHD[i].addEventListener('click', toggleItem, false);
}
function toggleItem() {
    var itemClass = this.parentNode.className;
    for (i = 0; i < accItem.length; i++) {
        accItem[i].className = 'accordionItem close';
    }
    if (itemClass == 'accordionItem close') {
        this.parentNode.className = 'accordionItem open';
    }
}

left-nav.html

<div class="left-nav">
    <div class="accordionItem close">
        <button class="accordionItemHeading has-dropdown">Menu Item 1</button>
        <div class="accordionItemContent">
            (Accordion Content)
        </div>
    </div>
    <div class="accordionItem close">
        <button class="accordionItemHeading has-dropdown">Menu Item 2</button>
        <div class="accordionItemContent">
            (Accordion Content)
        </div>
    </div>
</div>

left-nav.scss

.left-nav {
    .accordionItem {
        .accordionItemHeading {
            display: flex;
            justify-content: flex-start;
            align-items: center;
            font-weight: bold;
            font-size: 12px;
            line-height: 1.2;
            background: #fff;
            border: none;
            padding: 5px 0;
            color: purple;
            width: 100%;
            //text-align: left;
            outline: none;
            transition: 200ms;
            opacity: 1;
            &.has-dropdown {
                position: relative;
                &:before {
                    content: url('<caret-image-dn>');
                    transform: rotate(-90deg);
                    margin-right: 5px;
                    // position: absolute;
                    // left: 0;
                    // top: 10px;
                    // width: 16px;
                    // height: 100%;
                }
            }
        }
    }
    .close {
        float: none;
        &.accordionItem {
            opacity: 1;
        }
        .accordionItemContent {
            height: 0px;
            transition: height 1s ease-in-out;
            transform: scaleY(0);
            float: left;
            display: block;
        }
    }
    .open {
        &.accordionItem {
            opacity: 1;
            button.accordionItemHeading {
                &.has-dropdown {
                    &:before {
                        content: url('<caret-image-dn>');
                        transform: none;
                        // position: absolute;
                        // left: 0;
                        // top: 8px;
                        // width: 16px;
                        // height: 100%;
                    }
                }
            }
        }
        .accordionItemContent {
            transform: scaleY(1);
            transform-origin: top;
            transition: transform 200ms ease-in-out;   
        }
    }
}