Question

\ (\bbox [10pt, blue, border:5pt solid black]{\huge Hello}\)

Answer 1

In the preview window, these things do not always show up. You may need to do it in the post area.

\(\bbox [10pt, blue, border:5pt solid black]{\huge Hello}\)

Also, don't add a sapce between the \ and (.
`\(\bbox [10pt, blue, border:5pt solid black]{\huge Hello}\)`