The 25+5 clock I created as part of the FreeCodeCamp challenge was designed with React and vanilla CSS. I created an interface that includes two separate timer controls - one for a 25-minute work session and one for a 5-minute break. The user can start, pause, or reset the timers as needed. One of the key challenges I faced was implementing the logic to automatically switch between the work and break timers, but I was able to overcome this by using conditional rendering and state management techniques. Additionally, I included several features to enhance the user experience, such as audio alerts and a progress bar to display how much time is left.