Troubleshooting
Most "the theme is broken" reports turn out to be one of about a dozen things, and nearly all of them are diagnosable in under a minute once you know what to look at.
The pattern worth internalising: when something looks wrong, the question is rarely what is broken and usually which layer is this coming from. A Ghost site has four — your content, Ghost itself, the theme, and the browser in front of it — and a symptom that seems to belong to one very often belongs to another. A widget that renders blank is far more likely to be the widget's own script than any theme rule.
Signup and login are the exception that deserves its own method. Three separate things can break them, two of them fail silently, and the first one being wrong makes the other two untestable — so there is a diagnostic order, and following it turns an afternoon into a couple of minutes.