Using CSS to locate elements is causing issues with LocateAll

I am using LocateAll to find instances of an element on the page. I am using CSS as the primary way to locate my elements due to them being faster than xpath.

The following is the html:

<tbody xpath="1"><tr>
        <th></th>
        <th>
            PhoneNumber
        </th>
        <th>
            Address
        </th>
        <th>
            Id
        </th>
        <th>
            Gender
        </th>
        <th>
            Nickname
        </th>
        <th>
            Shipping
        </th>
        <th>
            Closed
        </th>
    </tr>
</tbody>

I want to grab all instances of "th". I am using the following method:

* def headerCount = karate.sizeOf(locateAll('tbody tr th'))

However, I am getting the following error:

org.graalvm.polyglot.PolyglotException: js eval failed twice:document.querySelector("tbody tr th[2]")['textContent'], error: [type: MAP, value: {type=object, subtype=error, className=DOMException, description=DOMException: Failed to execute 'querySelector' on 'Document': 'tbody tr th[2]' is not a valid selector.

I am assuming LocateAll works by indexing the locator to find all instances? If so, can I go an alternative route if possible (I'd rather not use xpath)?