Submit Button Don't work HTML

When you are making the form, you have typed: <form method="POST" action="" id="login>" To make the form working type the file name that contains the code to login for example:

<form method="POST" action="login_verify.php" id="login">
    <div class="input-group">
      <span class="input-group-addon" id="basic-addon1">
        <i class="fa fa-user" aria-hidden="true"></i></span>
      <input type="text" class="form-control" placeholder="Username" name="Username" aria-describedby="basic-addon1" required>
    </div>
    <div class="input-group"> 
      <span class="input-group-addon" id="basic-addon2">
        <i class="fa fa-key" aria-hidden="true"></i></span>
      <input type="password" class="form-control" placeholder="Password" name="Password" aria-describedby="basic-addon2" required>
    </div>
    <div class="text-center">
        <input type="submit" form="login" class="btn btn-success btn-submit" value="Login">
    </div>
</form>

A button located outside a form (but still a part of the form).

And you have a page in action attribute that receives the submitted field's value.

<form action="Your_Handle_Page" method="get" id="form1">
  First name: <input type="text" name="fname"><br>
  Last name: <input type="text" name="lname"><br>
</form>

<button type="submit" form="form1" value="Submit">Submit</button>

you haven't specify action on form submit you need to write redirect url in form action element as below.

<form method="POST" action="xyz.html" id="login">
    <div class="input-group">
      <span class="input-group-addon" id="basic-addon1">
        <i class="fa fa-user" aria-hidden="true"></i></span>
      <input type="text" class="form-control" placeholder="Username" name="Username" aria-describedby="basic-addon1" required>
    </div>
    <div class="input-group"> 
      <span class="input-group-addon" id="basic-addon2">
        <i class="fa fa-key" aria-hidden="true"></i></span>
      <input type="password" class="form-control" placeholder="Password" name="Password" aria-describedby="basic-addon2" required>
    </div>
    <div class="text-center">
        <input type="submit" form="login" class="btn btn-success btn-submit" value="Login">
    </div>
</form>