If you are using Constant Contact like in the example above, you can change the button color inside the editor. I’m not sure about the font but you should always be able to change it on your WordPress website via CSS. Here is a helpful article: https://createawebsitenow.com/custom-fonts-wordpress/

You can make changes to that via CSS. Examine the element with your browser developer tools to see which selectors are responsible for the styling. You then have to include the changes you make on your WordPress site either via a custom CSS functionality (e.g. inside the WordPress Customizer) or inside your active (child) theme.