Cross-browser bugs get easier when you reduce the page to the smallest failing example and compare computed styles instead of guessing from screenshots.

Process

1. Reproduce the issue in the target browser.
2. Remove unrelated layout and content.
3. Compare computed styles across browsers.
4. Add a fix at the smallest stable selector.

Autoprefixer

Autoprefixer will not fix every browser issue, but it removes a class of vendor-prefix problems that are not worth handling manually.