Add SCSS module for rules used on static sites

We're going to make the static sites depend on the main site's
stylesheet, but as part of that we need to be able to do a little bit of
customization specific to them - specifically, being able to bring over
the rules for setting up how lists and links look. Hopefully we
shouldn't need to use this much, but this is reasonable for now.

tildes/scss/modules/_static-site.scss

@@ -0,0 +1,14 @@
+// Copyright (c) 2019 Tildes contributors <code@tildes.net>
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+// Rules in this file are used by the Tildes static sites (Blog, Docs), not Tildes
+// itself. In general, rules in here should be kept to the absolute minimum, and only
+// used when necessary to transfer over styling to the static sites where it's not
+// feasible to do that through the separate CSS file in the repo for those sites.
+
+body.static-site {
+  main {
+    @extend %links-text;
+    @extend %lists-text;
+  }
+}

tildes/scss/styles.scss

@@ -27,6 +27,7 @@
 @import 'modules/sidebar';
 @import 'modules/site-footer';
 @import 'modules/site-header';
+@import 'modules/static-site';
 @import 'modules/tab';
 @import 'modules/text';
 @import 'modules/time';