[Theme Horse Support Team]

Hi titleboxing,
If you want to add css then you can add it from dashboard -> appearance -> theme options -> design options -> custom css
From here you just write the css.

The other way is that you just create a child theme and import the css.

/*
 Theme Name:   Interface Child
 Theme URI:    https://www.themehorse.com
 Description:  Theme Horse Child Theme
 Author:       Sunil JUng Chhetri
 Author URI:   http://example.com
 Version:      1.0.0
 Tags:         light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
 Text Domain:  Interface-child
*/

@import url("../interface/style.css");

/* =Theme customization starts here
-------------------------------------------------------------- */ 

Then activate your child theme and then you will be able to change the css

Thank you!