clear button havent color

hello i have a big problem.
my wordpress template has weird css and your plugin has a clear button. This button allows you to clear the wrong signature and start over. Unfortunately, this button has a white color + background. This button is not visible. I tried to change the color to directly in the php file contact-form-7-signature-addon/public/class-wpcf7-signature-public.php and even in css but unfortunately I don’t know in css. Can you please send me some css code or some instructions on how to set the word “Clear” to be black, for example