To avoid editing theme files, you can create a child theme very easily. Here’s an example using the Weaver Xtreme theme. Create wp-content/themes/weaver-xtreme-child/ and files style.css and functions.php.
Start style.css with the following header modified to match your situation.
/* Theme Name: Weaver Xtreme Child Theme URI: http://fordwebtech.com/blog/wp-content/themes/weaver-xtreme-child/ Description: Weaver Xtreme Child Theme Author: Phil Ford Author URI: http://fordwebtech.com/blog Template: weaver-xtreme Version: 1.0.0 License: GNU General Public License v2 or later License URI: http://www.gnu.org/licenses/gpl-2.0.html Tags: light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready Text Domain: weaver-xtreme-child */
Add custom css and php functions to the two files. Finally, activate the new Weaver Xtreme child theme which will now show up in the main dashboard theme picker.