By default when you create a child theme, the default CSS for the theme will always be loaded. This is the best way to create a child theme as it promotes proper child theme creation.
You should not be copy/pasting the entire CSS of the parent theme and modifying parts in your child theme. Instead you should use CSS selector specificity to override the default styles. If you absolutely must stop the default styles from loading, you can add the following to your child theme’s functions.php file.
/**
* Remove the CSS file for the parent theme.
*/
function my_child_theme_remove_parent_css() {
wp_dequeue_style( 'parent' ); // Please replace "parent" by the parent theme name.
}
add_action( 'wp_enqueue_scripts', 'my_child_theme_remove_parent_css', 11 );