<nav class="navbar navbar-expand-lg navbar-dark fixed-top bg-dark">
  <a class="navbar-brand" href="#">Sidebar Nav</a>
  <button
    class="navbar-toggler"
    type="button"
    data-toggle="collapse"
    data-target="#navbarCollapse"
    aria-controls="navbarCollapse"
    aria-expanded="false"
    aria-label="Toggle navigation"
  >
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarCollapse">
    <ul class="navbar-nav mr-auto sidenav" id="navAccordion">
      <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="#">Item 1</a>
      </li>
      <li class="nav-item">
        <a
          class="nav-link nav-link-collapse"
          href="#"
          id="hasSubItems"
          data-toggle="collapse"
          data-target="#collapseSubItems2"
          aria-controls="collapseSubItems2"
          aria-expanded="false"
        >Item 2</a>
        <ul class="nav-second-level collapse" id="collapseSubItems2" data-parent="#navAccordion">
          <li class="nav-item">
            <a class="nav-link" href="#">
              <span class="nav-link-text">Item 2.1</span>
            </a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">
              <span class="nav-link-text">Item 2.2</span>
            </a>
          </li>
        </ul>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Item 3</a>
      </li>
      <li class="nav-item">
        <a
          class="nav-link nav-link-collapse"
          href="#"
          id="hasSubItems"
          data-toggle="collapse"
          data-target="#collapseSubItems4"
          aria-controls="collapseSubItems4"
          aria-expanded="false"
        >Item 4</a>
        <ul class="nav-second-level collapse" id="collapseSubItems4" data-parent="#navAccordion">
          <li class="nav-item">
            <a class="nav-link" href="#">
              <span class="nav-link-text">Item 4.1</span>
            </a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">
              <span class="nav-link-text">Item 4.2</span>
            </a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">
              <span class="nav-link-text">Item 4.2</span>
            </a>
          </li>
        </ul>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Item 5</a>
      </li>
    </ul>
    <form class="form-inline ml-auto mt-2 mt-md-0">
      <input class="form-control mr-sm-2" type="text" placeholder="Search" aria-label="Search">
      <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
    </form>
  </div>
</nav>

<main class="content-wrapper">
  <div class="container-fluid">
    <h1>Main Content</h1>
  </div>
</main>

<footer class="footer">
  <div class="container">
      <div class="text-center">
          <span>Coded by <a href="https://si-dev.com/ru">SI-Dev</a>, 2018</span>
      </div>
  </div>
</footer>

html {
    position: relative;
    min-height: 100%;
}

body {
    padding-top: 4.5rem;
    margin-bottom: 4.5rem;
}

.footer {
  position: absolute;
  bottom: 0;
  width: 100%;
  height: 3.5rem;
  line-height: 3.5rem;
  background-color: #ccc;
}

.nav-link:hover {
  transition: all 0.4s;
}

.nav-link-collapse:after {
  float: right;
  content: '\f067';
  font-family: 'FontAwesome';
}

.nav-link-show:after {
  float: right;
  content: '\f068';
  font-family: 'FontAwesome';
}

.nav-item ul.nav-second-level {
  padding-left: 0;
}

.nav-item ul.nav-second-level > .nav-item {
  padding-left: 20px;
}

@media (min-width: 992px) {
  .sidenav {
    position: absolute;
    top: 0;
    left: 0;
    width: 230px;
    height: calc(100vh - 3.5rem);
    margin-top: 3.5rem;
    background: #343a40;
    box-sizing: border-box;
    border-top: 1px solid rgba(0, 0, 0, 0.3);
  }

  .navbar-expand-lg .sidenav {
    flex-direction: column;
  }

  .content-wrapper {
    margin-left: 230px;
  }

  .footer {
    width: calc(100% - 230px);
    margin-left: 230px;
  }
}

$(document).ready(function() {
  $('.nav-link-collapse').on('click', function() {
    $('.nav-link-collapse').not(this).removeClass('nav-link-show');
    $(this).toggleClass('nav-link-show');
  });
});