ATM application

We're going to build an application to track checking and savings account balances.

Specifications

You may edit the HTML file (but might not need to).

Users can deposit money into one of the bank accounts
Users can withdraw money from one of the bank accounts
- Make sure the balance in an account can't go negative. If a user tries to withdraw more money than exists in the account, ignore the transaction.
The color of a back account should reflect its balance. (There's a CSS class called .zero already written for this.)

By no means do you have to follow this. It's just here to help you get started if needed.

Note that these commits are all for the checking account only. Take this one account at a time.

Make the <body>'s background color turn red
Add a click listener to the checking account's "Deposit" button
- When you click the button it should console.log("hello")
On clicking "Deposit", it should get the user input
- Just console.log it
- You can save some time by hard-coding a value into the input box: <input value="something" />. That way you don't need to type stuff in all the time to test it.
On clicking "Deposit", it should update the "balance" with the user input
- Just make the user input show up. Don't worry about actually keeping track of a balance yet.
On "Deposit", it should get the current "balance"
- How can you get the content of the "balance" element?
- The content has a $ at the beginning of it, so Javascript will read it as text rather than as a number. How can you convert this text into a number?
On "Deposit", it updates the balance
- Now add the user input to the balance, and make it show up in the "balance" element
On "Withdraw", it updates the balance
- Follow the same steps as before, except you're subtracting instead of adding
Refactor the existing code
- Challenge: Try to have no function() that's longer than 5 lines. (Sandi Metz's Rule 2)

...then follow the same series of commits, but for the savings account.

What happens when the user wants to withdraw more money from the checking account than is in the account?
- If a withdrawal can be covered by the balances in both accounts, bring the withdrawn-from account down to $0 and take the remainder from the other account.
- If the withdrawn amount is more than the combined account balance, display an error.