Hello @viencentls, I am jrd10, not from the team. A user only 🙂.
I'm not sure to have understood your request.
For implementing the CCS which will avoid the underline,
On the application, click on the Options button (close to Files) > Theme > in the Text box Personalization,
add the code mentioned by David (above)
h1, h2, h3, h4 {
border-bottom: 0px !important;
}
And the titles will appear without the underline 🙂.
Have a good day.
José from France