If you wish to override some of the css/js files via a child theme, you may want to also prevent asset minification, which is enabled by default since v14. This can be achieved by a simple filter you can add to your child theme functions.php file:
add_filter('nectar_dev_mode', 'salient_child_dev_mode'); function salient_child_dev_mode() { return true; }
With the above set to true, all CSS and JS files will load from the relevant src directories rather than the build directories.