Is your feature request related to a problem? Please describe.
Right now the custom styles only apply to the public part

Describe the solution you'd like
I wish you could make custom styles in the configuration board

Describe alternatives you've considered
n/a

Additional context
Paid by aFFaC

Mockups:

Specs:

• Divide the current custom styles menu in two parts, same as has been done for custom fields (check screenshots)
• Add a custom styles editor in the admin. Specs for this.
• Apply custom styles in the admin bye adding the _custom_styles.html.erb partial