Split css (#1959)

Divides the css into sub-files and normalizes how colors are defined.

Co-authored-by: Joachim <joachim.robert@protonmail.com>

bookwyrm/templates/snippets/status/layout.html

@@ -4,7 +4,7 @@
 
 {% block card-header %}
 <div
-    class="card-header-title has-background-white-ter is-block"
+    class="card-header-title has-background-secondary is-block"
     {% if main %}id="anchor-{{ status.id }}"{% endif %}
 >
     {% include 'snippets/status/header.html' with status=status %}