Ein einfaches Child-Theme, das die CSS-Dateien über den optimalen Weg einbindet.

functions.php

<?php

function twentyfifteen_parent_enqueue_styles() {
	wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );
	wp_enqueue_style( 'google-font-cherry-swash', 'https://fonts.googleapis.com/css?family=Cherry+Swash:700' );
}
add_action( 'wp_enqueue_scripts', 'twentyfifteen_parent_enqueue_styles' );

style.css

/**
Theme Name: Adventskalender Advanced
Template: twentyFifteen
*/

.site-title {
	font-family: 'Cherry Swash', cursive;
}