diff --git a/inst/reveal.js-5.2.1/css/theme/source/ids.scss b/inst/reveal.js-5.2.1/css/theme/source/ids.scss
index e833b8f..f431662 100644
--- a/inst/reveal.js-5.2.1/css/theme/source/ids.scss
+++ b/inst/reveal.js-5.2.1/css/theme/source/ids.scss
@@ -366,6 +366,44 @@
   background: #{$idsOrange} !important;
 }
 
+// Adaptive vertical centering of slide content: the template groups each
+// slide's body content (everything after the heading block except speaker
+// notes) into a div.ids-slide-content. Slides carrying such a wrapper become
+// flex columns of full slide height: the heading block stays pinned to the
+// top and the wrapper's auto margins center the content in the remaining
+// space. Auto margins collapse to zero when there is no free space, so
+// packed slides still start directly below the heading and overflow
+// downwards as before -- the drawback that makes reveal.js' own `center`
+// option unusable here (it would also center the headings). The wrapper
+// keeps the footer band free (--ids-footer-reserve, published by the
+// template from the actual footer height), so centered content never
+// covers the footer; slides too packed to fit above it may, as they always
+// could. Display only ever changes for slides reveal.js is actually
+// showing, mirroring the section-divider rule above, which works the same
+// way; screen-only, so the pdf export keeps laying out slides itself.
+@media screen {
+  html .reveal .slides section:not(.stack):not(.title-frame) {
+    height: 100% !important;
+    display: flex !important;
+    flex-direction: column !important;
+  }
+
+  .reveal .slides section:not(.stack):not(.title-frame) > .ids-slide-content {
+    flex: none;
+    margin-top: auto !important;
+    margin-bottom: auto !important;
+    padding-bottom: var(--ids-footer-reserve, 48px);
+
+    // under block layout the first content element's margin-top collapsed
+    // with the heading's margin-bottom; as flex items the two would add up
+    // instead, so drop it and let the heading spacing rule alone define
+    // the gap, as before
+    > :first-child {
+      margin-top: 0 !important;
+    }
+  }
+}
+
 .reveal .slides section.level1:not(.title-frame) > h1:first-child {
   text-align: center !important;
   margin: 0 !important;
diff --git a/inst/reveal.js-5.2.1/dist/theme/ids.css b/inst/reveal.js-5.2.1/dist/theme/ids.css
index dd54e86..8d56808 100644
--- a/inst/reveal.js-5.2.1/dist/theme/ids.css
+++ b/inst/reveal.js-5.2.1/dist/theme/ids.css
@@ -523,6 +523,40 @@
   content: none !important;
 }
 
+/* Adaptive vertical centering of slide content: the template groups each
+   slide's body content (everything after the heading block except speaker
+   notes) into a div.ids-slide-content. Slides carrying such a wrapper become
+   flex columns of full slide height: the heading block stays pinned to the
+   top and the wrapper's auto margins center the content in the remaining
+   space. Auto margins collapse to zero when there is no free space, so
+   packed slides still start directly below the heading and overflow
+   downwards as before -- the drawback that makes reveal.js' own `center`
+   option unusable here (it would also center the headings). The wrapper
+   keeps the footer band free (--ids-footer-reserve, published by the
+   template from the actual footer height), so centered content never
+   covers the footer; slides too packed to fit above it may, as they always
+   could. Display only ever changes for slides reveal.js is actually
+   showing, mirroring the section-divider rule above, which works the same
+   way; screen-only, so the pdf export keeps laying out slides itself. */
+@media screen {
+  html .reveal .slides section:not(.stack):not(.title-frame) {
+    height: 100% !important;
+    display: flex !important;
+    flex-direction: column !important;
+  }
+
+  .reveal .slides section:not(.stack):not(.title-frame) > .ids-slide-content {
+    flex: none;
+    margin-top: auto !important;
+    margin-bottom: auto !important;
+    padding-bottom: var(--ids-footer-reserve, 48px);
+  }
+
+  .reveal .slides section:not(.stack):not(.title-frame) > .ids-slide-content > :first-child {
+    margin-top: 0 !important;
+  }
+}
+
 :root {
   --r-bold-color: #f6a800;
   --r-list-bullet-color: #f6a800;
diff --git a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
index 45b55e4..f5eb25b 100644
--- a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
+++ b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
@@ -1177,6 +1177,72 @@
   })();
 </script>
 <script>
+  // Adaptive vertical centering of slide content: slides with little content
+  // look lost when everything is glued below the title bar, while packed
+  // slides must start at the top. Reveal.js' own `center` option cannot do
+  // this -- it also vertically centers the headings. Instead, each slide's
+  // body content (everything after the heading block, except speaker notes)
+  // is grouped into a .ids-slide-content wrapper here, and the ids theme
+  // turns these slides into flex columns: the heading stays at the top, and
+  // the wrapper's auto margins center it in the remaining space. Auto
+  // margins collapse to zero when there is no free space, so packed slides
+  // still start directly below the heading and overflow downwards exactly
+  // as before. The wrapper also reserves the footer band (--ids-footer-
+  // reserve, published below from the actual footer height), so centered
+  // content never reaches into the footer; slides too packed to fit above
+  // it may, as they always could.
+  (function () {
+    // The footer is viewport-fixed and display:none on the title page;
+    // express its height (plus the dotted rule, the progress bar and a
+    // little air) in slide coordinates, where the theme consumes it.
+    function publishFooterReserve() {
+      var footer = document.getElementById('ids-footer');
+      if (!footer || typeof Reveal === 'undefined') return;
+      var prevDisplay = footer.style.display;
+      footer.style.display = 'block';
+      var px = (footer.offsetHeight + 10) / (Reveal.getScale() || 1);
+      footer.style.display = prevDisplay;
+      document.documentElement.style.setProperty('--ids-footer-reserve', px + 'px');
+    }
+
+    // number of leading elements forming the heading block: the slide title
+    // (h1/h2) and, on level-2 slides, an h3 framesubtitle following it
+    function headingCount(slide) {
+      var kids = slide.children;
+      if (!kids[0] || (kids[0].tagName !== 'H1' && kids[0].tagName !== 'H2')) return 0;
+      if (kids[0].tagName === 'H2' && kids[1] && kids[1].tagName === 'H3') return 2;
+      return 1;
+    }
+
+    function wrapSlideContent(slide) {
+      if (slide.dataset.contentWrapped) return;
+      slide.dataset.contentWrapped = '1';
+      var content = Array.prototype.filter.call(
+        Array.prototype.slice.call(slide.children, headingCount(slide)),
+        function (el) { return el.tagName !== 'ASIDE'; }
+      );
+      // heading-only (divider) and empty slides keep their dedicated layout
+      if (!content.length) return;
+      var wrapper = document.createElement('div');
+      wrapper.className = 'ids-slide-content';
+      slide.insertBefore(wrapper, slide.children[headingCount(slide)] || null);
+      content.forEach(function (el) { wrapper.appendChild(el); });
+    }
+
+    function build() {
+      if (typeof Reveal === 'undefined' || !Reveal.isReady()) return;
+      publishFooterReserve();
+      Reveal.getSlides().forEach(wrapSlideContent);
+    }
+
+    if (typeof Reveal !== 'undefined') {
+      if (Reveal.isReady()) build();
+      else Reveal.addEventListener('ready', build);
+      Reveal.addEventListener('resize', publishFooterReserve);
+    }
+  })();
+</script>
+<script>
   // Practice/read-aloud view: pressing 'r' toggles a single scrollable page
   // containing every slide's content and speaker notes. Text-to-speech
   // browser extensions cannot walk a reveal.js deck (hidden slides are
@@ -1195,13 +1261,19 @@
         section.className = 'ids-transcript-slide';
         var heading = slide.querySelector('h1,h2');
         if (heading) section.appendChild(heading.cloneNode(true));
-        Array.prototype.forEach.call(slide.childNodes, function (node) {
+        function appendContent(node) {
           if (node.nodeType !== Node.ELEMENT_NODE) return;
           if (node.tagName === 'ASIDE' || node.tagName === 'H1' ||
               node.tagName === 'H2' || node.tagName === 'SECTION' ||
               (node.classList && node.classList.contains('ids-overview-toc'))) return;
+          if (node.classList && node.classList.contains('ids-slide-content')) {
+            // the adaptive-centering wrapper is transparent for the transcript
+            Array.prototype.forEach.call(node.childNodes, appendContent);
+            return;
+          }
           section.appendChild(node.cloneNode(true));
-        });
+        }
+        Array.prototype.forEach.call(slide.childNodes, appendContent);
         var notes = Array.prototype.map.call(
           slide.querySelectorAll('aside.notes'),
           function (n) { return n.innerHTML; }