Fix playground example (#1928)

Reviewed-by: Titus Wormer <tituswormer@gmail.com>

Author: VitorLuizC

docs/playground.server.mdx

@@ -13,7 +13,8 @@ export const playgroundSource = `Hello, world!
 Below is an example of markdown in JSX.
 
 <div style={{padding: '1rem', backgroundColor: 'violet'}}>
-Try and change the background color to \`tomato\`.`
+  Try and change the background color to \`tomato\`.
+</div>`
 
 # Playground