diff --git a/.github/workflows/website.yml b/.github/workflows/website.yml
index e49b506..441da2b 100644
--- a/.github/workflows/website.yml
+++ b/.github/workflows/website.yml
@@ -59,7 +59,7 @@ jobs:
 
       - name: Restore R Cache
         if: steps.check-rmd.outputs.count != 0
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ${{ env.R_LIBS_USER }}
           key: ${{ runner.os }}-${{ hashFiles('.github/R-version') }}-1-${{ hashFiles('.github/depends.Rds') }}
diff --git a/slideshow/Makefile b/slideshow/Makefile
index 30abfbe..8e66e51 100644
--- a/slideshow/Makefile
+++ b/slideshow/Makefile
@@ -1,2 +1,2 @@
 index.html: slides.md Makefile
-	pandoc --to=revealjs --standalone -o $@ --css=mywhite.css  $<
+	pandoc --to=revealjs --standalone -o $@ --css=mywhite.css  $< && sed -i 's|\^4//|^4/|g' index.html
diff --git a/slideshow/index.html b/slideshow/index.html
index 3c03260..649fbbe 100644
--- a/slideshow/index.html
+++ b/slideshow/index.html
@@ -8,8 +8,8 @@
   <meta name="apple-mobile-web-app-capable" content="yes">
   <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
   <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no, minimal-ui">
-  <link rel="stylesheet" href="https://unpkg.com/reveal.js@^4//dist/reset.css">
-  <link rel="stylesheet" href="https://unpkg.com/reveal.js@^4//dist/reveal.css">
+  <link rel="stylesheet" href="https://unpkg.com/reveal.js@^4/dist/reset.css">
+  <link rel="stylesheet" href="https://unpkg.com/reveal.js@^4/dist/reveal.css">
   <style>
     .reveal .sourceCode {  /* see #7635 */
       overflow: visible;
@@ -19,12 +19,18 @@
     div.columns{display: flex; gap: min(4vw, 1.5em);}
     div.column{flex: auto; overflow-x: auto;}
     div.hanging-indent{margin-left: 1.5em; text-indent: -1.5em;}
-    ul.task-list{list-style: none;}
+    /* The extra [class] is a hack that increases specificity enough to
+       override a similar rule in reveal.js */
+    ul.task-list[class]{list-style: none;}
     ul.task-list li input[type="checkbox"] {
+      font-size: inherit;
       width: 0.8em;
       margin: 0 0.8em 0.2em -1.6em;
       vertical-align: middle;
     }
+    .display.math{display: block; text-align: center; margin: 0.5rem auto;}
+    /* CSS for syntax highlighting */
+    html { -webkit-text-size-adjust: 100%; }
     pre > code.sourceCode { white-space: pre; position: relative; }
     pre > code.sourceCode > span { display: inline-block; line-height: 1.25; }
     pre > code.sourceCode > span:empty { height: 1.2em; }
@@ -88,9 +94,8 @@
     code span.va { color: #19177c; } /* Variable */
     code span.vs { color: #4070a0; } /* VerbatimString */
     code span.wa { color: #60a0b0; font-weight: bold; font-style: italic; } /* Warning */
-    .display.math{display: block; text-align: center; margin: 0.5rem auto;}
   </style>
-  <link rel="stylesheet" href="https://unpkg.com/reveal.js@^4//dist/theme/black.css" id="theme">
+  <link rel="stylesheet" href="https://unpkg.com/reveal.js@^4/dist/theme/black.css" id="theme">
   <link rel="stylesheet" href="mywhite.css"/>
 </head>
 <body>
@@ -338,12 +343,12 @@ <h1>Send me a PR!</h1>
     </div>
   </div>
 
-  <script src="https://unpkg.com/reveal.js@^4//dist/reveal.js"></script>
+  <script src="https://unpkg.com/reveal.js@^4/dist/reveal.js"></script>
 
   <!-- reveal.js plugins -->
-  <script src="https://unpkg.com/reveal.js@^4//plugin/notes/notes.js"></script>
-  <script src="https://unpkg.com/reveal.js@^4//plugin/search/search.js"></script>
-  <script src="https://unpkg.com/reveal.js@^4//plugin/zoom/zoom.js"></script>
+  <script src="https://unpkg.com/reveal.js@^4/plugin/notes/notes.js"></script>
+  <script src="https://unpkg.com/reveal.js@^4/plugin/search/search.js"></script>
+  <script src="https://unpkg.com/reveal.js@^4/plugin/zoom/zoom.js"></script>
 
   <script>
 
