How to setup CSP policy in Keycloak Welcome Page?

I have setup CSP in all realms, and it works as long as the URL already contains realms name.
My problem is the welcome page doesn’t belong to any realms and use Keycloak default CSP policy.

content-security-policy: frame-src 'self'; frame-ancestors 'self'; object-src 'none';

How to setup CSP policy in Keycloak Welcome Page?