jsFiddle is the perfect solution; it provides a custom environment (based on user selections) to test (or fiddle with) your JavaScript, HTML, and CSS ... code in the appropriate areas of the page.

The vulnerability can be exploited by loading an HTML page that uses specially crafted CSS code. The CSS code isn't very complex and tries to apply a CSS effect known as backdrop-filter to a ...

But CSS Exfil is not an infallible method. It can only steal HTML attributes found on the page at load time, and not from dynamically injected code after the initial page load. Gualtieri argues ...