Tower Defense with a twist: all towers must be positioned with CSS Flexbox
Great job!  Couple suggestions:<p>1) When roads twist around on themselves, draw a bridge or some other kind of hint to indicate the path invaders will follow (e.g. <a href="https://i.imgur.com/t3fuboT.png" rel="nofollow">https://i.imgur.com/t3fuboT.png</a>).  In Wave 9 it wasn't clear they'd take the long way through the loop.<p>2) When the tab goes into the background, pause the game instead of erasing the user's entire tower layout and progress.<p>Also a general observation / opinion: Does anyone else feel like flexbox syntax is unintuitive?  I feel like you could achieve the same thing without rotating axes, and with more consistent naming conventions.