Ask HN: What is the best visual diff program for web pages?

Hi HN! I've been thinking a lot about visual diffs recently for web pages. I know there are tools like Chromatic Storybook[0] that take image snapshots of a page and then render pixel differences, but I couldn't find tools that actually render live React components or web pages and display them side-by-side, highlighting the differences.

Do people know if these tools exist? If they do, what are some of the best tools out there?

To clarify, the goal is not to compare source code, but to compare the rendered HTML/CSS output.

[0]: https://www.chromatic.com/