More formatting needed on inline thank you message

Really need this feature added. We have our HubSpot form on a black background on our site. Once a customer submits their information to sign up to our newsletter, they do not see our thank you message!

I have attempted to add custom css code:

.submitted-message {
color: white !important;
}

But this does not override the color of the message.

From reading other posts, this seems to be an ongoing concern for users dating back to last year!

@ Hubsport Support Team, has this been resolved? Have you found a workaround in the meantime?