As an example, I wanted to create a custom, more compact style sheet for JIRA (I don’t understand all those products with complex interfaces AND white space everywhere). I failed. It’s a PITA to write any selector and it wouldn’t survive the next build from the devs.
You don't have to select things based on CSS selectors. If you something really resilient, you select something based on the content of the elements (a button that says "Send" will rarely change to say something else, while the styling/DOM can change a lot). Otherwise xpath is another option of the DOM doesn't change a lot while CSS class/ID attributes changes between builds.
