Pouvez vous m'aider , je ne comprend pas . Je pense que j'ai la bonne code mais pour mettre h2 en bleu mais quand j'exécute il m'envoi un erreur h2 pas bleu

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).