JSFiddle - React, Tailwind, and code Playground

by neonDog

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css">
<div class="form-mod">
    <div>
        <form class="form-inline justify-content-center">
            <div class="form-group">
                <div>
                    <input type="text" name="email" value="" placeholder="Enter your email..." class="form-control">
                </div>
            </div>
            <div class="form-group">
                <button type="submit" class="btn btn-primary">Request an Invite</button>
            </div>
        </form>
    </div>
</div>

CSS

.form-mod {
  display: inline-block;
  text-align: center;
  padding: 16px 32px;
  background: rgba(0, 0, 0, 0.2);
  border-radius: 3;
  box-shadow: 0 20px 63px 0 rgba(0,0,0,.6);

  [type="text"] {
    width: 260px;
    margin-right: 16px;
    border-radius: 100px;
    padding-left: 18px;
    border-radius: $border-radius;
    font-size: 16px;
  }

  @include media-breakpoint-down(sm) {
    .form-group {
      width: 100%;
    }
    [type="text"] {
      width: 100%;
      margin: 0 0 16px 0;
      display: block;
    }
    opacity: .5;
  }
}

/* NEW */
.form-group {
  flex: 1 0 auto;
}