<header>
  <div class="container">
    <nav class="navbar navbar-expand-md">
      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbar-example-03" aria-controls="navbar-example-03" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>

      <div class="collapse navbar-collapse" id="navbar-example-03">
        <ul class="navbar-nav mr-auto ml-auto">
          <li class="nav-item active">
            <a cla