Fix build.sh for ubuntu & CSS change for jagon with pop-ups

Ubuntu's default shell (ie what you get with #!/bin/sh) is dash, not bash. This is a much stricter implementation of the POSIX standard and causes all sorts of headaches when scripts assume /bin/sh == /bin/bash.

I've fixed the build.sh to work in dash, and verified it still works in bash so it should still work fine for you Mac folk.

I've also added some CSS to the jargon with pop-up to change the mouse cursor.