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 de961f5..c1068ac 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
@@ -819,9 +819,54 @@
 
 
 /*********************************************
- * ARROWS and SLIDE NUMBERS
+ * FULLSCREEN TOGGLE
  *********************************************/
 
+// Small fixed toggle for touch devices (script injected by default.html):
+// phones have no F11 and the browser chrome eats slide pixels. Hidden on
+// pointer devices (F11 exists there) and whenever the Fullscreen API is
+// unavailable -- the script also removes it then. Same muted look and column
+// as the slide menu button, one slot above it.
+#ids-fullscreen {
+  display: none;
+  position: fixed;
+  left: 30px;
+  bottom: 6%;
+  z-index: 30;
+  width: 28px;
+  height: 28px;
+  border: 0;
+  padding: 0;
+  cursor: pointer;
+  opacity: 0.55;
+  // Feather-style corner brackets; gray idle, IDS orange while fullscreen
+  // (the two data URIs differ only in the stroke colour).
+  background: transparent url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23aaaaaa' stroke-width='2.5' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M8 3H5a2 2 0 0 0-2 2v3'/%3E%3Cpath d='M16 3h3a2 2 0 0 1 2 2v3'/%3E%3Cpath d='M8 21H5a2 2 0 0 1-2-2v-3'/%3E%3Cpath d='M16 21h3a2 2 0 0 0 2-2v-3'/%3E%3C/svg%3E") center / contain no-repeat;
+
+  &:active,
+  &:focus-visible {
+    opacity: 0.9;
+  }
+
+  &.is-fullscreen {
+    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23f6a800' stroke-width='2.5' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M8 3H5a2 2 0 0 0-2 2v3'/%3E%3Cpath d='M16 3h3a2 2 0 0 1 2 2v3'/%3E%3Cpath d='M8 21H5a2 2 0 0 1-2-2v-3'/%3E%3Cpath d='M16 21h3a2 2 0 0 0 2-2v-3'/%3E%3C/svg%3E");
+  }
+}
+
+// Only touch devices get the button; desktops keep their F11.
+@media (hover: none) and (pointer: coarse) {
+  #ids-fullscreen {
+    display: block;
+  }
+}
+
+// position:fixed elements repeat on every printed page -- never print it.
+html.reveal-print #ids-fullscreen {
+  display: none !important;
+}
+
+
+
  .reveal .controls .controls-arrow:after, .reveal .controls .controls-arrow:before {
   width: 13px !important; /* size */
   height: 4px; /* line width */