Add Zenburn theme

I was doing some work on an old site over the weekend that uses this
color scheme and it reminded me how much I used to like it. Might as
well!

tildes/scss/styles.scss

@@ -46,3 +46,4 @@
 @import "themes/dracula";
 @import "themes/atom_one_dark";
 @import "themes/solarized";
+@import "themes/zenburn";

tildes/scss/themes/_zenburn.scss

@@ -0,0 +1,41 @@
+// Color palette is Jani Nurminen's "Zenburn"
+// http://kippura.org/zenburnpage/
+
+// Basic monochrome colors
+$background: #3f3f3f;
+$background-alt: #4f4f4f;
+$foreground: #dcdccc;
+$foreground-alt: #aaa;
+$border: #5b605e;
+
+// Accent colors
+$blue: #8cd0d3;
+$green: #7f9f7f;
+$green-bright: #80d4aa;
+$pink: #dca3a3;
+$red: #dc8c6c;
+$purple: #bc8cbc;
+$yellow: #efef8f;
+
+// Actual theme definition
+$theme-zenburn: (
+  "alert": $green-bright,
+  "background-primary": $background,
+  "background-secondary": $background-alt,
+  "border": $border,
+  "comment-label-exemplary": $blue,
+  "comment-label-joke": $green,
+  "comment-label-noise": $yellow,
+  "comment-label-offtopic": $pink,
+  "comment-label-malice": $red,
+  "error": $red,
+  "foreground-primary": $foreground,
+  "foreground-secondary": $foreground-alt,
+  "link": $blue,
+  "link-visited": $purple,
+  "warning": $yellow,
+);
+
+body.theme-zenburn {
+  @include use-theme($theme-zenburn);
+}

tildes/tildes/templates/base.jinja2

@@ -28,6 +28,8 @@
   <meta name="theme-color" content="#282c34">
   {% elif request.cookies.get('theme', '') == 'black' %}
   <meta name="theme-color" content="#222">
+  {% elif request.cookies.get('theme', '') == 'zenburn' %}
+  <meta name="theme-color" content="#3f3f3f">
   {% endif %}
 
   {% assets "css" %}
@@ -113,7 +115,8 @@
             ("dark", "Solarized Dark"),
             ("dracula", "Dracula"),
             ("atom-one-dark", "Atom One Dark"),
-            ("black", "Black")) %}
+            ("black", "Black"),
+            ("zenburn", "Zenburn")) %}
         <option value="{{ theme }}"
           {{ 'selected' if theme == request.cookies.get("theme", "white") else '' }}
         >

tildes/tildes/views/settings.py

@@ -39,6 +39,7 @@ def get_settings(request: Request) -> dict:
         "dracula": "Dracula",
         "atom-one-dark": "Atom One Dark",
         "black": "Black",
+        "zenburn": "Zenburn",
     }
 
     if site_default_theme == user_default_theme: