JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>

<menu>
  <li>Menu 1</li>
  <li>Menu 2</li>
  <li class="adressbar">
     <input type="text" value="Etwas Text"/>
  </li>
  <li>Auswahl</li>
</menu>

CSS

menu {
    background-color: #eee;
    padding: 0.5em 0;
    display: -webkit-box;
    display: -moz-box;
    display: -ms-box;
    display: box;
    -webkit-box-align: center;
    list-style-type: none;
}

menu li {    
    padding: 0 0.5em;
}

menu li.adressbar {    
    -webkit-box-flex: 1;
    -moz-box-flex: 1;
    -ms-box-flex: 1;
     box-flex: 1;
}

menu .adressbar input {
    width: 100%;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    -ms-box-sizing: border-box;
    box-sizing: border-box;
    border: 1px solid black;
    font-size: 1em;
    line-height: 1em;
}