Fix closing tag mismatch

index.html

@@ -35,7 +35,7 @@
                         This contains some katex.
                         `$$\cfrac{(v, c) \Downarrow v'}{(v, c) \rightarrow v'}$$`
                     </textarea>
-                </script>
+                </section>
             </div>
         </div>
         <script src="node_modules/reveal.js/dist/reveal.js"></script>