[Theme Horse Support Team]

Hi James,

If you really want to make changes only in css then you may add your CSS via Custom CSS. Goto dashboard -> appearance-> theme options -> design options -> Custom css and add your custom css.

If you like to make a child theme then you need to add the following css in your functions.php
wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );

hope this may help you
or you may add in your child theme of style.css

/*
Theme Name: Ultimate Child Theme
Author: Self-Help WordPress User
Template: Ultimate Pro child
*/

@import url("../ultimate-pro/style.css");
.wrapper {
width: 95%;
background-color: #fff;
}

Thank you!