Hey there, I think you did a wonderful job. Seriously I really love your site, everything about it is simple yet cool.
Anyways, here are my suggestions:
1- After a user (adds) enters a to do, I think it would be cool if you cleared the field automatically so the user can enter a new one comfortably instead of clearing it again.
2- It would be also cool if you made it more visible when a user is trying to edit one of the todos. At first I really thought it wasn't working til I directly clicked on it and tried to edit it myself. I think you can achieve that by maybe making the input edit field bigger? Idk just a suggestion.