Modify Widget Style/Look

I’d like to modify the look of the widget. Where would I do that? In the widget-recent-global-posts.php file? If so, do I just re-upload it to the mu-plugins folder for it to work? Specifically, I’d like the text to top-align with the top of the avatar, and I’d like to remove the
that appears before the first post, thus pushing the content down further in that widget then content in other widgets.