Hello, @chafike,
Thanks for the screenshot. I have understood your issue.
Now, in order to solve your issue simply go to the Dashboard >> XStore >> Theme OPtions >> Theme Custom CSS >> Global and then paste the below code at the bottom of the CSS box there.
.etheme-above-checkout-form .woocommerce-message{background:green !important;padding:40px !important;}
Then save settings and check back to your site after clearing the browser cache. The result will appear like this: https://postimg.cc/VSkzm3P6
Regards 8Themes Team.