Fix incorrect HTML code example (tailwindlabs#1962)

Fixes tailwindlabs#1959.

Author: wongjn

src/docs/styling-with-utility-classes.mdx

@@ -864,7 +864,7 @@ Here's what a `btn-primary` class might look like, using [theme variables](/docs
 
 ```html
 <!-- [!code filename:HTML] -->
-<button class="btn-primary">Save changes</button>
+<button class="btn-primary">
   Save changes
 </button>
 ```