Create a child theme

Child theme folder to include:

Style.css file:

Theme Name: Twenty Fifteen Child Theme

description: >-

A child theme of the Twenty Fifteen default WordPress theme

Author: Nick Schäferhoff

Template: twentyfifteen

Version: 1.0.0

Functions.php file:

<?php

add_action( ‘wp_enqueue_scripts’, ‘my_theme_enqueue_styles’ );

function my_theme_enqueue_styles() {

wp_enqueue_style( ‘parent-style’, get_template_directory_uri() . ‘/style.css’ );

}

Refer to: