js-code

<script>
document.addEventListener("DOMContentLoaded", function(event) { 


var acc = document.getElementsByClassName("accordion");
var panel = document.getElementsByClassName('panel');

for (var i = 0; i < acc.length; i++) {
    acc[i].onclick = function() {
        var setClasses = !this.classList.contains('active');
        setClass(acc, 'active', 'remove');
        setClass(panel, 'show', 'remove');

        if (setClasses) {
            this.classList.toggle("active");
            this.nextElementSibling.classList.toggle("show");
        }
    }
}

function setClass(els, className, fnName) {
    for (var i = 0; i < els.length; i++) {
        els[i].classList[fnName](className);
    }
}

});
</script>

<script>
/* Toggle between adding and removing the "active" and "show" classes when the user clicks on one of the "Section" buttons. The "active" class is used to add a background color to the current button when its belonging panel is open. The "show" class is used to open the specific accordion panel */
var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i++) {
    acc[i].onclick = function(){
        this.classList.toggle("active");
        this.nextElementSibling.classList.toggle("show");
};
}

</script>