hugo-PaperMod/layouts/partials/header.html

{{- if eq .Site.Params.defaultTheme "auto" }}
<script>
    if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
        document.body.classList.add('dark');
    }
</script>
{{- end }}
<header class="header">
    <nav class="nav">
        <p class="logo"><a href="{{ "" | absLangURL }}">{{ .Site.Title }}</a></p>

        {{- $currentPage := . }}
        <ul class="menu" id="menu" onscroll="menu_on_scroll()">
            {{- range .Site.Menus.main }}
            {{- $menu_item_url := .URL | relLangURL }}
            {{- $page_url:= $currentPage.RelPermalink | relLangURL }}
            <li>
                <a href="{{ .URL | absLangURL }}">
                    <span {{- if eq $menu_item_url $page_url }}
                        {{- /* the menu item links to the current page (with relLangURL) */}} class="active" {{- end }}>
                        {{ .Name }}
                    </span>
                </a>
            </li>
            {{- end }}
        </ul>
    </nav>
</header>