Oleh Denysenko developed front-end features for two repositories, focusing on responsive design and component reusability. For MarneyDude/404_not_found, he built a mobile menu component using HTML and CSS, implementing overlay functionality, structured navigation, and action buttons to enhance mobile usability and establish a scalable UI pattern. In Arinalekseewa/Portfolio-Jefferson, he delivered a hero section with retina-ready backgrounds and interactive social links, addressing image path reliability and ensuring consistent rendering across devices. His work demonstrated a solid grasp of front-end development principles, emphasizing maintainable code and cross-device compatibility, though the scope was limited to feature delivery without bug fixes.