onClick div addClass and remove class without jQuery

Facing Javascript issue on Wordpress child-theme editor try to
create onClick div addClass and removeClass like
https://www.traveloka.com/en-my/ website tab's white container with background opacity on my Wordpress testing website ...

" onClick div addClass and removeClass " is anyone can fix it ...

Visit testing-website.

Already done with CSS... Only Javascript issue...javascript

<-- onClick addClass CSS --> ( _1a8i5 _20Et3 )

.LbQ-i._1a8i5 {
    z-index: 103;
}
.LbQ-i._20Et3:before {
    opacity: .92;
    pointer-events: all;
    z-index: -1;
}

This is my wrong Javascript code here...
Not sure what code can be use it if-statement for-loop or else ...

document.getElementsByClassName("bv1w6e3rg").addEventListener("click",function(){
     var element = document.getElementsByClassName("LbQ-i");
     element.classList.add("_20Et3 _1a8i5");
});