Very Very Minimalist Pomodoro Clock - looking for feedback

Here’s the link: http://codepen.io/LordMathis/full/ggYqdx/
I’ve used CSS Flexbox and JQuery

It is very clean. I liked the addition of the notification. However, some users may opt to block notifications.

While the design is sleek, users may be confused as to how to start or pause the clock. Users may also miss the ability to reset the clock.

Nice work!