In March 2025, Kattsoff developed a new design token for the VKCOM/vkui-tokens repository, introducing calendarColorSidebarItemBackground to enhance calendar sidebar theming. By defining light and dark theme states along with normal, hover, and active backgrounds, Kattsoff improved UI consistency and enabled more flexible, token-driven customization for calendar components. The work leveraged CSS, JavaScript, and TypeScript, focusing on scalable theming architecture and commit-driven development. This addition expanded design token coverage, simplified future branding updates, and reduced styling overhead, demonstrating a thoughtful approach to maintainable front-end development and UI theming without introducing major bugs during the implementation period.