That is beautiful! One thing I've noticed tho from some of my older users is that they have no idea what the difference is between "login" and "sign up". I'm sure there's a better way to present that, but I haven't figured out how so far.
I would wonder how many users notice the "Sign Up" link or read it as "Sign In" and not understand how to proceed.
The distinction between username and email is lost on a lot of people, unless you expect accounts to outlive emails and the value of having an account is worth this friction (think Dropbox or online banking) then use an email or phone instead.
I do wonder if for most apps a two-step process is easier: enter your email/phone to continue, if that exists ask them to logon or otherwise create an account. I realize there are concerns about account enumeration, which are valid, but end up being overly hostile to the user (plus most registration flows leak anyway).
Wouldn't fit in the UI as designed unless you broke each button into two lines though.
Step 2: if that email exists in the database, ask for password. Otherwise confirm with the user that they are new to the site. Then ask for password twice.
Step 3: done.
I avoid it and have found people are far less confused