homework done

[Anny523925]

New:

• Sign In & Sign Up page can be switched by the blue font at the bottom
• All requirements for the third and fourth weeks have been completed
• The third row in Sign Up changed to password and added a complexity validation function
• Sign Up page linked to a mock server, when testing, need to use 'node server.js' start the server
• The first row in Sign In not change the name to 'username', but it already map to username: 'emilys' for test