cullmann.io/themes/blowfish/layouts/partials/toc.html

<details open id="TOCView"
  class="toc-right mt-0 overflow-y-scroll overscroll-contain scrollbar-thin scrollbar-track-neutral-200 scrollbar-thumb-neutral-400 dark:scrollbar-track-neutral-800 dark:scrollbar-thumb-neutral-600 rounded-lg ltr:-ml-5 ltr:pl-5 rtl:-mr-5 rtl:pr-5 hidden lg:block">
  <summary
    class="block py-1 text-lg font-semibold cursor-pointer bg-neutral-100 text-neutral-800 ltr:-ml-5 ltr:pl-5 rtl:-mr-5 rtl:pr-5 dark:bg-neutral-700 dark:text-neutral-100 lg:hidden">
    {{ i18n "article.table_of_contents" }}
  </summary>
  <div
    class="min-w-[220px] py-2 border-dotted ltr:-ml-5 ltr:border-l ltr:pl-5 rtl:-mr-5 rtl:border-r rtl:pr-5 dark:border-neutral-600">
    {{ .TableOfContents | emojify }}
  </div>
</details>
<details class="toc-inside mt-0 overflow-hidden rounded-lg ltr:-ml-5 ltr:pl-5 rtl:-mr-5 rtl:pr-5 lg:hidden">
  <summary
    class="py-1 text-lg font-semibold cursor-pointer bg-neutral-100 text-neutral-800 ltr:-ml-5 ltr:pl-5 rtl:-mr-5 rtl:pr-5 dark:bg-neutral-700 dark:text-neutral-100 lg:hidden">
    {{ i18n "article.table_of_contents" }}
  </summary>
  <div
    class="py-2 border-dotted border-neutral-300 ltr:-ml-5 ltr:border-l ltr:pl-5 rtl:-mr-5 rtl:border-r rtl:pr-5 dark:border-neutral-600">
    {{ .TableOfContents | emojify }}
  </div>
</details>

<script>

  var margin = 200;
  var marginError = 50;

  (function () {
    var $window = $(window);
    var $toc = $('#TOCView');
    var tocHeight = $toc.height();

    function onResize() {
      var windowAndMarginHeight = $window.height() - margin;
      if(tocHeight >= windowAndMarginHeight) {
        $toc.css("overflow-y", "scroll")
        $toc.css("max-height", (windowAndMarginHeight + marginError) + "px")
      } else {
        $toc.css("overflow-y", "hidden")
        $toc.css("max-height", "9999999px")
      }
    }

    $window.on('resize', onResize);
    $(document).ready(onResize);
  })();

{{ if .Site.Params.smartTOC }}

  (function () {
    var $toc = $('#TableOfContents');
    if ($toc.length > 0) {
      var $window = $(window);

      function onScroll() {
        var currentScroll = $window.scrollTop();
        var h = $('.anchor');
        var id = "";
        h.each(function (i, e) {
          e = $(e);
          if (e.offset().top - $(window).height()/3 <= currentScroll) {
            id = decodeURIComponent(e.attr('id'));
          }
        });
        var active = $toc.find('a.active');      
        if (active.length == 1 && active.eq(0).attr('href') == '#' + id) return true;

        active.each(function (i, e) {
          {{ if .Site.Params.smartTOCHideUnfocusedChildren }} 
            $(e).removeClass('active').siblings('ul').hide();
          {{ else }}
            $(e).removeClass('active');
          {{ end }}
        });
        $toc.find('a[href="#' + id + '"]').addClass('active')
        $toc.find('a[href="#' + id + '"]').parentsUntil('#TableOfContents').each(function (i, e) {
          $(e).children('a').parents('ul').show();          
        });
      }

      $window.on('scroll', onScroll);
      $(document).ready(function () {
        {{ if .Site.Params.smartTOCHideUnfocusedChildren }} 
          $toc.find('a').parent('li').find('ul').hide();
        {{ end }}
        onScroll();
      });
    }
  })();
{{ end }}

</script>