Css issues on Appointment paypal button


I have an urgency issue. I have set the appointment calendar, which is here:

The big problem, is that, the "Please confirm 40€ payment for maintenance web 1h" button, is white(background color) . Style doesnt wants to understand the css style of the general input.. and when i change the ".app_submit_btn" css.. it´s not working also...

I have also changed of template..just to check if it wasn´t a code from there that wasn´t making the trouble... and color stayed the same..That mean that css issues is from the plugin. and i don´t know how to change it ..

Can you help me ? I want to display it to guest my clients to apply. They are waiting for me to send the planning.

I can´t leave it like this, cause we don´t see the button.

Thank you very much !