<nav id="site-navigation" class="main-navigation" role="navigation">
<!--changed class from container nav-bar to nav-bar to make it fullwidth-->
<div class="nav-bar">
the thing is: it works on every page of the site but the home page. On the home, the navigation still has the container class and I don¨t understand why. Doesn´t it get it´s header from the same header.php as all the other pages?
Also, always do your code level customization using the Child theme, Child Themes « WordPress Codex so that the changes will be there, even after the update.
Let us know if you have any other questions in a separate thread.