The thing is though, as soon as you take it out of context (change the DOM structure, drop the nearby styles that don't directly target that element, etc) thing

The thing is though, as soon as you take it out of context (change the DOM structure, drop the nearby styles that don't directly target that element, etc) things are often going to stop behaving the way you want. At that point you honestly just have to know how to work with CSS for real if you want to get the desired outcome, which makes me skeptical of a tool that claims to let you clip out a piece of the page with all the CSS behavior intact