This is cool, but it bothers me that the inhale cycle doesn't end with completely filling the circle with blue. I feel unfulfilled, like when the DVD player screensaver doesn't hit neatly into the corner of the screen when it totally looks like it's going to
I think it's because you're not supposed to expand your lungs so much that they feel like they're going to burst.
But if you scroll to the bottom of the css and look at line 69, you can change transform: scale(90%); to transform: scale(100%); to see if you like it better.