I Got the main structure and general css styles at first glance and that reduces time to think about placing elements and stuff.
What challenges did you encounter, and how did you overcome them?not actually that big, but I got a bit confused on how to get the content of the input boxes and the tip percentage every time one of them changes value, it was pretty javascripty, but it works at least.
What specific areas of your project would you like help with?i think that there can be less javascript code to do the job, i might have taken the long way.