Added just-the-docs-default.scss which includes the theme set in _config.yml

_includes/head.html

@@ -12,12 +12,7 @@
 
   <link rel="shortcut icon" href="{{ 'favicon.ico' | absolute_url }}" type="image/x-icon">
 
-  {% if site.color_scheme == nil or site.color_scheme == "nil" %}
-    {% assign color_scheme = 'light' %}
-  {% else %}
-    {% assign color_scheme = site.color_scheme %}
-  {% endif %}
-  <link rel="stylesheet" href="{{ color_scheme | prepend: '/assets/css/just-the-docs-' | append: '.css' | absolute_url }}">
+  <link rel="stylesheet" href="{{ '/assets/css/just-the-docs-default.css' | absolute_url }}">
 
   {% if site.ga_tracking != nil %}
     <script async src="https://www.googletagmanager.com/gtag/js?id={{ site.ga_tracking }}"></script>

_sass/color_schemes/dark.scss

-// override this file to change the dark theme
-
 $body-background-color: $grey-dk-300;
 $sidebar-color: $grey-dk-300;
 $border-color: $grey-dk-200;

_sass/color_schemes/light.scss

-// override this file to change the light (default) theme

assets/css/just-the-docs-default.scss

+---
+---
+{% if site.color_scheme and site.color_scheme != "nil" %}
+  {% assign color_scheme = site.color_scheme %}
+{% else %}
+  {% assign color_scheme = "light" %}
+{% endif %}
+{% include css/just-the-docs.scss.liquid color_scheme=color_scheme %}