Finch analyses and works with the existing code in the page and tries really hard to make the new changes as close to the original code. New code is added only in the cases where there was none before. For example, if you add/change some style to a button that is defined in your CSS, the properties will be changed/added to the button's CSS class. If you want to change a unique button in a unique page, then a new selector and code will be added.