In your functions.php of your child theme, check the code lines for custom.css and responsive.css in alx_styles.
if ( ot_get_option('responsive') != 'off' ) { wp_enqueue_style( 'responsive', get_template_directory_uri().'/responsive.css' ); }
if ( ot_get_option('custom') == 'on' ) { wp_enqueue_style( 'custom', get_template_directory_uri().'/custom.css' ); }Should look like that (excerpt you may want to change get_template_directory depending on which files you want to load from the child theme)