Fix: (css.html) Unify types (#434)

Previously a slice holding a string was being appended to slices of
resource.Resources, which could cause an error in the build process.
Now resource.Resources are used for all of these files.

Author: alphapapa

layouts/partials/css.html

@@ -22,8 +22,8 @@
 <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Noto+Sans+Symbols+2">
 
 <!-- Process and include Sass files. -->
-{{- $sass := (slice "theme-css/pst/pydata-sphinx-theme.scss")
-           | append (resources.Match "theme-css/*.scss")
+{{- $sass := append (resources.Get "theme-css/pst/pydata-sphinx-theme.scss")
+                    (resources.Match "theme-css/*.scss")
            | append (resources.Match "css/*.scss") -}}
 
 {{- range $sass -}}