The PayPal button and drop down menu styles are inherited from your theme. If it does not look right for some reason, it is a theme problem, not a plugin problem.
If you are not familiar with CSS please contact your theme developer or provider. If you are unable to contact your theme developer or provider feel free to send us an email and we can fix it for you for free.
If you are familiar with CSS you should be able to use a browser inspector, usually via F12, to identify the problem. Once you have identified the problem, and found a solution you need to override the style. Many themes include a custom CSS section in the their admin screen where you can enter CSS. If not, I would recommend installing the plugin Simple Custom CSS: https://wordpress.org/plugins/simple-custom-css.