The inputs for range voting custom labels are not using OOUI at the moment:
They should be updated to do so (this happens in ./modules/ext.securepoll.htmlform/page.create.js and in ./includes/HtmlForm/HTMLFormRadioRangeColumnLabels.php). You can check out T272378: SecurePoll: Custom column labels do not appear (or do not appear correctly) [8h] for some additional context. You will probably have to use a layout to re-wrangle the table in OOUI.





