问bootstrap 4:巨型加速器中的居中内联表单

EN

<div class="jumbotron" id="home">
  <h1 class="display-3">My Awesome App!</h1>
  <p class="lead">This is why you should download this fantastic app!</p>
  <hr class="my-4">
  <p>Want to know more? Join our mailing list!</p>
  <form class="form-inline">
    <label class="sr-only" for="yourEmail">Email</label>
    <div class="input-group mb-2 mr-sm-2 mb-sm-0">
      <div class="input-group-addon">@</div>
      <input type="text" class="form-control" id="yourEmail" placeholder="Your Email">
    </div>
    <button type="button" class="btn btn-primary my-2 my-sm-0">Sign Up</button>
  </form>
</div>

body{
  position: relative;
}

#home{
  background-image: url('../img/jumbotron-bkg-2.jpg');
  margin-top: 50px;
  text-align: center;
}

#yourEmail{
  width: 350px;
}

#about h2, #about-summary{
  text-align: center;
}

.card{
  margin-bottom: 30px;
}

.card img{
  height: 350px;
  width: 100%;
}

#cards-container{
  margin-bottom: 50px;
  padding: 20px 40px;
}

#download{
  text-align: center;
  padding-top: 100px;
  padding-bottom: 150px;
  background-color: #0afff2;
}