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.
So you can use the button once to paste your html. Then make sure you start after the second set of bacticks and then use the button again so you can paste in your css
See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (').