Result Component with React & CSS Modules

Took this opportunity to have a bit of practice with React (boy, it's been a while)!

My main issue was implementing a transition effect on the submit button's background color on hover.

Initially, I applied it via transition: backrgound-color 0.2s on the .btn default state but this turned out janky (it looked like the button flashed on mouse-enter and the transition only triggered on mouse-leave).

A bit of searching tells me that I can use the CSSTransition component for this.

Is this the best way to add transition effects into React or is there a native way to do it?