There are many ways to make a fixed navbar stay inside a parent's div container. We'll go over the most straightforward one here.

Imagine you have the following code, modified slightly from the Bootstrap docs:

<div class="container">
  <nav class="navbar navbar-fixed-top navbar-inverse bg-inverse">
    <button class="navbar-toggler hidden-lg-up" type="button" data-toggle="collapse" data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
    </button>
    <div class="collapse navbar-toggleable-md" id="navbarResponsive">
      <a class="navbar-brand" href="#">
        <img src="" width="30" height="30" class="d-inline-block align-top" alt="">Navbar
      </a>
      <ul class="nav navbar-nav float-md-right">
        <li class="nav-item active">
          <a class="nav-link" href="#">Home
            <span class="sr-only">(current)</span>
          </a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Link</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">Link</a>
        </li>
      </ul>
    </div>
  </nav>
  <div class="next"></div>
  hello
</div>
div.next {
  background-color: lightblue;
  width: 100%;
  height: 60rem;
}

And your page looks like this:

Solutions

While the docs read "Navbars and their contents are fluid by default. Use optional containers to limit their horizontal width," the easiest solution is to use CSS to set the width of the navbar directly:

div.next {
  background-color: lightblue;
  width: 100%;
  height: 60rem;
}

.container {
  padding: 0px;
}

nav.navbar {
  width: inherit;
  top: 0%;
  left: 50%;
  transform: translateX(-50%);
}

By adding rules targeting .container and nav.navbar, your navbar is now the same width as the parent's container: