Wordpress with Javascript

Question

Hi i tried a accordion in wordpress home page which works when a button is clicked some content to show below with css and javasrcipt, but to me its not working. Here is the CSS

 button.accordion {
    background-color: #eee;
    color: #444;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    text-align: left;
    border: none;
    outline: none;
    transition: 0.4s;
}

button.accordion.active, button.accordion:hover {
    background-color: #ddd;
}

div.panel {
    padding: 0 18px;
    background-color: white;
     max-height: 0;
    overflow: hidden;
    transition: 0.6s ease-in-out;
    opacity: 0;
}    

div.panel.show {
    opacity: 1;
    max-height: 500px; 
}

Here is the js

 <script type="text/javascript">
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>

I tried to include the js in the header.php but not working while all the css are working fine Thanks.