ヘッダーにbootstrapを使う

bootstrapcdnから、cssのパスを取得します。
https://www.bootstrapcdn.com/

https://stackpath.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css

cdn読み込みを書きます。

<link rel="stylesheet" type="text/css" href="https://stackpath.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" />

documentのnavsを参考に当てはめていきます。
http://getbootstrap.com/docs/4.0/components/navs/

<link rel="stylesheet" type="text/css" href="https://stackpath.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" />
<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="">管理画面</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarText" aria-controls="navbarText" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse" id="navbarText">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">予約状況 <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">予約入力</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">出欠勤登録</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">予約実績</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">個別データ</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">IPアドレス管理</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">スタッフ管理</a>
      </li>
    </ul>
    <ul class="nav justify-content-end">
    <li class="nav-item">
    	<a class="nav-link disabled" href="#">ログアウト</a>
  	</li>
    </ul>
  </div>
</nav>
hogehoge

初期

bootstrap使用後

非常に良い！