I'm a CSS/HTML novice and I haven't really found how to do this by searching. I have a simple login page where a person enters in a username and password. The page has a large background image. I want to create a rounded box that the two text fields (username and password) and the submit button goes into and sits on top of to further separate form the background image. Here is the main part of the html file, I just want to know what should I put into the container section of the CSS file to get a rounded white box .

```
<div class="container">

  <form class="form-signin" role="form" name='f'   
action='${pageContext.request.contextPath}/j_spring_security_check' method='POST'>
    <h2 class="form-signin-heading">Please sign in</h2>
    <input type='text' name='j_username' class="form-control" placeholder="Username" 
required autofocus>
    <input type='password' name='j_password' class="form-control" 
placeholder="Password" required>
    <div class="checkbox">
      <label>
        <input type="checkbox" value="remember-me"> Remember me
      </label>
    </div>
    <button class="btn btn-lg btn-primary btn-block" type="submit">Sign in</button>
  </form>

```