Style Fields in Contact Form

RE: tried to insert some code of this site

Unfortunately you can’t just cut and paste code from ??https://contactform7.com/styling-contact-form/. You need to prepare code that works for your particular WP site and to do that you usually need to understand what you are doing.

There is a link at the bottom of the page to a comprehensive and detailed article on Styling Contact Form 7 Forms. The article shows people, with suitable HTML & CSS skills, how to change the appearance of their Contact Form 7 Forms to meet their particular requirements.

Also use Firebug or Chrome Dev Tools to examine the HTML and CSS of your CF7 form in detail. Once you understand how the HTML and CSS is configured in your CF7 form, you should be able to see the CSS changes you need to change the appearance of the form to suit your requirements.