_navbar.html

<div class="navbar navbar-default  navbar-fixed-top" role="navigation">
  <div style="background:white">
  </div>
  <div class="container">
    <div class="navbar-header">
      <!-- NOTE: add "navbar-inverse" class for an alternate navbar background -->
      <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#navbar">
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand navbar-img" href="#">
        <div class="d-flex align-items-center h-25">
          <img src="figures/bioinf-fr-logo-blau.svg" class="d-flex align-items-center" alt="">
        </div>

      </a>
              <a class="navbar-brand">Optimierung</a>

    </div>
    <div id="navbar" class="navbar-collapse collapse">
      <ul class="nav navbar-nav">
        <li><a href="index.html">Intro</a></li>
        <li><a href="exercise-sheet-1.html">AB 1</a></li>
        <li><a href="exercise-sheet-2.html">AB 2</a></li>
        <li><a href="exercise-sheet-3.html">AB 3</a></li>
        <li><a href="exercise-sheet-4.html">AB 4</a></li>
        <li><a href="exercise-sheet-5.html">AB 5</a></li>

      </ul>
      <ul class="nav navbar-nav navbar-right">
        <li><a href="http://www.bioinf.uni-freiburg.de/index.html?en2">Contact</a></li>
      </ul>
    </div><!--/.nav-collapse -->
  </div><!--/.container -->
</div><!--/.navbar -->