<!--Trigger-->
<a class="login-trigger" href="#" data-target="#login" data-toggle="modal">Login</a>

<div id="login" class="modal fade" role="dialog">
  <div class="modal-dialog">
    
    <div class="modal-content">
      <div class="modal-body">
        <button data-dismiss="modal" class="close">&times;</button>
        <h4>Login</h4>
        <form>
          <input type="text" name="username" class="username form-control" placeholder="Username"/>
          <input type="password" name="password" class="password form-control" placeholder="password"/>
          <input class="btn login" type="submit" value="Login" />
        </form>
      </div>
    </div>
  </div>  
</div>
body{
  height: 100vh;
  text-align: center;
}
  /*Trigger Button*/
.login-trigger {
  font-weight: bold;
  color: #fff;
  background: linear-gradient(to bottom right, #B05574, #F87E7B);
  padding: 15px 30px;
  border-radius: 30px;
  position: relative; 
  top: 50%;
}

/*Modal*/
h4 {
  font-weight: bold;
  color: #fff;
}
.close {
  color: #fff;
  transform: scale(1.2)
}
.modal-content {
  font-weight: bold;
  background: linear-gradient(to bottom right,#F87E7B,#B05574);
}
.form-control {
  margin: 1em 0;
}
.form-control:hover, .form-control:focus {
  box-shadow: none;  
  border-color: #fff;
}
.username, .password {
  border: none;
  border-radius: 0;
  box-shadow: none;
  border-bottom: 2px solid #eee;
  padding-left: 0;
  font-weight: normal;
  background: transparent;  
}
.form-control::-webkit-input-placeholder {
  color: #eee;  
}
.form-control:focus::-webkit-input-placeholder {
  font-weight: bold;
  color: #fff;
}
.login {
  padding: 6px 20px;
  border-radius: 20px;
  background: none;
  border: 2px solid #FAB87F;
  color: #FAB87F;
  font-weight: bold;
  transition: all .5s;
  margin-top: 1em;
}
.login:hover {
  background: #FAB87F;
  color: #fff;
}
Run Pen

External CSS

  1. https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js
  2. https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js