Pomodoro React App

👋 I will be updating this app (refactoring state using Redux, writing more tests), so I am interested in any and all feedback!

• The timer mode is controlled by a form containing three radio inputs. There's no submit button because the form is never meant to be submitted. What's the best approach to this accessibility issue?
• Why is Firefox rendering my colors differently than Chrome/Safari?
• Is there too much transition bling on the buttons?