Help with (re)building forms from the Theme Manager

As I am still learning Wappler and super enthousiastic about the recently (expirementally) added Theme Manager, I have been trying to rebuild the “Invalid input” form and “Input addons” form of “Bootstrap 4 Preview.html” page and came across a few problems I could use some help with:

1. How can I select/find an existing class? For example “form-control is-invalid” class for the “Text Input” element in the “Invalid input form”?

2. How can I add global attributes, like the “$” and “.00” spans inline with the “Text Input” field in the “Input addons” form?

3. For global attributes like the above, there is a “Lang” value that can be set. How are languages/translations of these attributes setup and managed?

4. Last quick question: Where are the Sand Serif / Monospace fonts in theme manager used for? Is it recommended to set a font there, despite they are empty on default themes?

Thanks for any help or explanation in advance!