On clicking 'Careers', 'Mentorship' and 'Meetups' in the navbar

[zhangtreefish]

Expected: After clicking 'Careers', 'Mentorship' and 'Meetups' in the navbar, new content of the clicked tabs renders, while the clicked elements stay put.

What happened: these clicked elements shift rightward on larger view ports and leftward on smaller ones before and then revert to their initial positions over the course of 1-2 seconds while the new content renders. At the meantime, the at the upper right corner (if a user was logged in) was replaced by 'Log In' and 'Sign Up'.

How to reproduce: https://udacity-client.herokuapp.com/, IE, firefox, or Chrome.