Hi @hongbicchu and welcome to our community!
There’s a syntax issue with the h3 element. Compare the element tags with the p element below it (which has the correct syntax).
For future reference, we encourage you to post your actual code, rather than a screenshot.
When you enter a code block into a forum post, please precede it with three backticks to make it easier to read.
You can also use the “preformatted text” tool in the editor (</>) to add the backticks.
See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (').