Yah, as Shinobody said, the text is too large for your textboxes. Could be a browser issue (Chrome) I couldn't even read the level numbers. I found the 'levels' concept to be annoying and break up the game. One 'endless' level where the difficulty increases would have been much better. You could have had a time counter and added 'checkpoints' at every 1 minute interval instead.
Also, adding in different shapes and rotations and directions of movement would be a really easy way to change this game from boring to fun, especially since this game type has been done many times before... you really need to add something new.