Container with rounded corners and title has bad position

[merwok]

Describe the bug
On firefox, container rounded with title has an unwanted border.

To Reproduce

    <div class="nes-container is-rounded with-title">
      <h1 class="title">Not found!</h1>
      <p>Sorry, the requested page does not exist.</p>
    </div>

Observed issue with and without is-centered.

Expected behavior
Get a container with rounded corners + title displayed interrupting the top border.

Screenshots

Testing on demo site (by adding a class using DOM inspector) does not show the problem:

Environment:

• OS: Debian testing
• Browser: Firefox 68.2.0esr

Suggestion(s) for fixing this issue
I haven’t redefined text size for root element, so with browser defaults the margin-top of -1.5rem is not enough to end up at the right place to cover the border. -1.6rem does the trick.

I am already redefining some style from nes.css (to avoid white background), so I may change this too to have -2rem which looks great to me 😎