Submit button behavior

I’m using contact form 7-everything seems to be working(happy days).
For Submit I’m using my custom image with bit of transition and opacity effect(when hover).

What I want to add there is:
When all required fields are filled correctly I would like to bring opacity of submit button to 1. (that would help user to know that all fields are correct and form is ready to be submitted).

Is there any class or ID I can target it with CSS something like .submit.correct Fields{opacity:1;}?

thanks

my site link is:https://webdesignz.eu/blog/index.php/contact/

https://www.ads-software.com/extend/plugins/contact-form-7/