Hugo-theme-stack/layouts/partials/comments/provider/utterances.html

<script src="https://utteranc.es/client.js" 
        repo="{{ .Site.Params.comments.utterances.repo }}"
        issue-term="{{ .Site.Params.comments.utterances.issueTerm }}"
        {{ with .Site.Params.comments.utterances.label }}
        label="{{ . }}"
        {{ end }}
        crossorigin="anonymous"
        async
        >
</script>

<style>
    .utterances {
        max-width: unset;
    }
</style>

<script>
    function setUtterancesTheme(theme) {
        let utterances = document.querySelector('.utterances iframe');
        if (utterances) {
            utterances.contentWindow.postMessage(
                {
                    type: 'set-theme',
                    theme: `github-${theme}`
                },
                'https://utteranc.es'
            );
        }
    }

    addEventListener('message', event => {
        if (event.origin !== 'https://utteranc.es') return;
        setUtterancesTheme(document.body.dataset.scheme)
    });

    window.addEventListener('onColorSchemeChange', (e) => {
        setUtterancesTheme(e.detail)
    })
</script>