<form>
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp">
    <small id="emailHelp" class="form-text text-muted">We'll never share your email with anyone else.</small>
  </div>
  <div class="form-group">
    <label for="exampleInputPassword1">Password</label>
    <input type="password" class="form-control" id="exampleInputPassword1">
  </div>
  <div class="form-group form-check">
    <input type="checkbox" class="form-check-input" id="exampleCheck1">
    <label class="form-check-label" for="exampleCheck1">Check me out</label>
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

<div class="input-group mb-3">
  <input type="text" class="form-control rounded-left" placeholder="Recipient's username" aria-label="Recipient's username" aria-describedby="basic-addon2">
  <div class="input-group-append">
    <span class="input-group-text rounded-right" id="basic-addon2">@example.com</span>
  </div>
</div>
<div class="input-group mb-3">
  <div class="input-group-prepend">
    <button class="btn btn-primary dropdown-toggle rounded-left" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Dropdown</button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Action</a>
      <a class="dropdown-item" href="#">Another action</a>
      <a class="dropdown-item" href="#">Something else here</a>
      <div role="separator" class="dropdown-divider"></div>
      <a class="dropdown-item" href="#">Separated link</a>
    </div>
  </div>
  <input type="text" class="form-control rounded-right" aria-label="Text input with dropdown button">
</div>