Language problem and color change

Hello,
When I use the add-on "Opt-in Form" in the pagebuilder it shows the language in Dutch.
When I use the module SP-Page-Builder and the add-on "Opt-in Form" it shows the language in English.
Please see the attachment.
Is it possible to translate the module with the add-on, and where?

Then, the confirmation color is green.
I tried to change the color to white, but nothing happens.

.sppb-alert-success {
    background:#000000!important;
    color: #FFFFFF!important;
}

Can you help please?
Regards, Peter