Styling for LockStep message

[hirokiterashima]

I added an ability for steps to lock and show a message to the students:
4de27ab

You just need to call Node.prototype.disableInteractivity = function(doDisable, message)

See step 1.1 here for example: http://wise-qa.berkeley.edu/webapp/preview.html?projectId=4743

The problem is, it's ugly. When you get a chance, please style this so we don't have students puking in class.