By default you can’t add HTML to a Widget Title in WordPress, such as a break tag <br>, you can get around this by adding a filter to allow shortcode to the title area….

In functions.php file in your child theme add:

add_filter('widget_title', 'do_shortcode');

add_shortcode('br', 'ng_shortcode_breaktag');
function ng_shortcode_break( $attr ){ 
	return '<br />'; 
}

Now in your Widget Title area just use [br] where you want the HTML break.

You can also add a span element using the same technique, then target that in CSS to do what you got to do.

add_filter('widget_title', 'do_shortcode');


add_shortcode('span', 'ng_shortcode_spantag');
function ng_shortcode_spantag( $attr, $content ){ 
return '<span>'. $content . '</span>'; 
}

Now in your Widget Title area just use [span]part of the title[/span] where you want the span tag to wrap around.