sekret

index.html

<div id="f" class='root'>
    <div id="g">
        <div id="k">foo</div>
    </div>
</div>
<div id='diag'>
    kkkkk

</div>

playground.json

{
    "scripts": [],
    "styles": []
}

script.js

let elt = document.querySelector('#k')
let diag = document.querySelector('#diag')

function log(s) {
    diag.appendChild(document.createTextNode( s + ' '))
}
log(elt)

function getParent(elt, sel) {
    let dad
    let putativeParents = document.querySelectorAll(sel)
    dad = elt
    while(1) {
        dad = dad.parentNode
        for (e of putativeParents) {
            if (e == dad) { return dad  }
        }
        if (dad.tagName == 'HTML') { break }
    }
    alert('fail')
}

let dad = getParent(elt, '#f')
log(dad)

style.css

#diag { color: red }