Custom slick-theme.css

Hi @cleforweb,
there are several ways to achieve this. The “smartest” one is probably to copy slick-theme.css to your Child Theme’s css folder and add the following to your function.css:

add_action( 'wp_enqueue_scripts', function() {
	wp_add_inline_style( 'slick-slider-core-theme', file_get_contents( get_stylesheet_directory() . "/css/slick-theme.css" ) );
}, 11 );

Note that by using wp_add_inline_style() your CSS will be printed inline in your document.

You might also use:

add_action( 'wp_enqueue_scripts', function() {
	wp_deregister_style( 'slick-slider-core-theme' );
	wp_register_style( 'slick-slider-core-theme', get_stylesheet_directory_uri() . "/css/slick-theme.css", array( 'slick-slider-core' ), '1.6.0' );
}, 11 );

But doing so, you’ll need to manually add the “Helper CSS” to your document (see the FAQ question “Is it possible to prevent the plugin from adding additional helper CSS on my page?”).

Alternatively, you may use the “Additional CSS” section of the Customizer.