In June 2025, Graouts expanded test coverage for CSS marker animations in the mozilla/gecko-dev repository, focusing on the ::marker pseudo-element and its animation properties. Using HTML and web platform testing skills, Graouts authored Web Platform Tests to validate parsing and computed values for animation-range, animation-range-start, animation-range-end, and animation-timeline. This work improved regression safety and enabled earlier detection of issues, supporting safer feature shipping and better cross-browser compatibility. By linking tests to Bug 1973475 and a related WebKit export pull request, Graouts ensured strong traceability and alignment across browser engines, deepening the reliability of CSS animation features.