Hello,
I am using a lot of modals with Forge over the bridge-API.
https://developer.atlassian.com/platform/forge/apis-reference/ui-api-bridge/modal/
It seems, that the documented token and CSS variable --elevation-surface-current is not properly set for these modals and appears to be default surface instead of surface-overlay.
The token is documented here: https://atlassian.design/components/tokens/all-tokens#utility