Customise SEND button

Hans, I believe these are the two css class selectors you want to edit:
.wpcf7-submit {}
.wpcf7-submit:hover {}

Sorry. I could not find them. Where exactly should I look? Cheers.

You could add the custom css into your child theme‘s stylesheet. For some themes, you can add custom css through the theme options. There are also some plugins for adding custom css.

Here’s an article that might help:
https://www.wpbeginner.com/wp-tutorials/how-to-style-contact-form-7-in-wordpress/