Non-selectable headlines in "select multiple" form field?

Hello!

Our form is located here: https://www.leadingpractice.com/become-a-member/access-to-industry-standards/

If you take a look at the “I would like to get access to the following Enterprise Standard(s):*” form field, I have inserted “-” characters to indicate a new area from which people can choose from.

I would like to insert something like headlines instead of the “-” character, but the headlines should not be selectable.

Is it possible to do this?

Thank you!

https://www.ads-software.com/plugins/si-contact-form/