Text decoration properties highlighted red in Webflow code editor

Hello folks,
I’m trying to underline a text with some custom code and i see Webflow highlights it in red as if it’s an invalid property. Any idea why? This underline also doesn’t display in Safari and I don’t understand why.

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

For more context: is-underlined is added as a combo class
Screenshot 2023-03-20 at 14.43.35