Style Radio Buttons inside Edit Page (Custom Fields)

Add your styles to /your-theme/admin-edit-post.css

.inside ul.acf-radio-list.radio.horizontal li label {
 /* styles... */
}

Then enqueue the styles by adding this to your theme’s functions.php:

function wpse250000_admin_styles( $hook ) {
    // Bail if we're not on the post.php admin page
    if ( 'post.php' !== $hook ) {
        return;
    }

    // Ensure we're looking at a post. Add other post types to array if desired.
    $post_type = get_post_type();
    if ( ! $post_type || ! in_array( $post_type, [ 'post' ] ) ) {
        return;
    }

    wp_enqueue_style( 'admin-edit-post-styles', get_template_directory_uri() . '/admin-edit-post.css' );
}
add_action( 'admin_enqueue_scripts', 'wpse250000_admin_styles' );