Invalid theme folder: _sass no change on theme addition

I am sorry if this issue has been under ad nauseam discussions but I am building my first site with Jekyll (placed in Github pages), and I have stumbled on this problem, which I can’t seem to find the solution after significant time of debugging reading and trying some modifications on the code. The problem is that even trying both installation of locally added themes and remote there is no change, the site simply keeps its plain HMTL apperance. Some more info that I suspect that might be related here: Invalid theme folder: _sass Remote Theme: Using theme mmistakes/so-simple-theme Jekyll. Obviously, I am trying to use the remote way of this theme but no luck.

The issue is actually in your layout:

    <head>
        <meta charset="utf-8">
        <title>{{ page.title }}</title>
        <link rel="stylesheet" href="/assets/css/styles.scss">
    </head>

Browsers cannot load .scss files.
So should load the compiled CSS file instead:

<link rel="stylesheet" href="/assets/css/styles.css">

Hi,
I hope that was the problem alas my file in ./_layouts/default.html is pointing to the CSS file as you mention:

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>{{ page.title }}</title>
    <link rel="stylesheet" href="/assets/css/styles.css">
  </head>
  <body>
    {% include navigation.html %}
    {{ content }}
  </body>
</html>

BTW, I should have said before probably, I built the site by following the step-by-step tutorial in Jekyll’s page.

I don’t know if this fix is related to my issue, but it seems to add the theme alas I am missing my navigation layout.

So, has the issue resolved now?

No, it only resolves in the Home page, not the entire website.

Can you post an URL each, to resolved page and to non-resolved page…?