Worked on the Skyscanner/backpack repository to address portal rendering issues in BpkPopover and BpkDatepicker components, focusing on improving stability for iframe-embedded deployments and during the React 17 to 18 migration. Applied React and TypeScript to synchronize the isOpen prop bidirectionally and ensure renderTarget was correctly forwarded, particularly for desktop popovers. Broadened renderTarget typing to support various runtime scenarios and aligned it with BpkDatepicker usage. Enhanced test coverage by adding comprehensive regression and desktop-path tests, and refined Jest configuration and mocks to stabilize test execution. The work reduced rendering regressions and improved test reliability in frontend development workflows.