Couple of suggestions

- Use `document.querySelector`/`document.querySelectorAll` instead of `document.getElementById`/`document.getElementsByClassName`
 [MDN link](https://developer.mozilla.org/en-US/docs/Web/API/document.querySelector)
- Make it a habit to pass a radix whenever you use `parseInt()` for readability sake.
[MDN link](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt#Parameters)
- You could use the `+` operator instead of `parseInt`, since `parseInt` is weird at times. For eg. Try `parseInt(10-10-10, 10)`. What did you get? No `NaN`???? :open_mouth: What the hell!!!!
    You got `10` instead. But why is that? Bcoz `parseInt` parses up to the first date separator (`-` or `/`) snd throws out the rest.  _Atleast thats what I tell myself_ :stuck_out_tongue:
- Also this is how a pull request works. I forked your repo. Did some changes on my branch(`suggestions`), committed the changes and sent  pull request to your repo's `master` branch. Now you may merge the PR or close it without merging. Its your choice :smile: