During March 2025, this developer enhanced the VKCOM/vkui-tokens repository by introducing a new design token, calendarColorSidebarItemBackground, to support calendar sidebar theming. The work focused on defining light and dark theme states, as well as normal, hover, and active backgrounds for sidebar items, ensuring consistent and accessible UI styling across themes. Leveraging CSS, JavaScript, and TypeScript, the developer expanded the design token architecture to simplify future branding updates and accelerate theming iterations. This contribution improved UI consistency for calendar components and established a clearer path for token-driven customization, while demonstrating a strong grasp of front-end theming and token lifecycle management.