option to use gradient backgrounds

app/templates/archive.html

@@ -1,6 +1,16 @@
 {% extends "base.html" %}
 {% block head %}
 <title>{{ settings.SITENAME }}</title>
+{% if week_background %}
+<style>
+body {
+    background: {{ week_background }};
+}
+</style>
+<script>
+    window.useHue = true;
+</script>
+{% endif  %}
 {% endblock %}
 {% block content %}
     <div class="index archive">

app/templates/item.html

@@ -13,6 +13,22 @@
     <meta property="og:url" content="{{ url }}"/>
     {% endif %}
     <meta property="og:site_name" content="{{ settings.SITENAME }}"/>
+{% if item.use_hue %}
+<style>
+:root {
+    --color1: var(--bg);
+    --color2: var(--bg);
+    --color3: var(--bg);
+}
+body {
+    background: linear-gradient(to bottom, var(--color1), var(--color2), var(--color3));
+}
+</style>
+<script>
+    window.useHue = true;
+</script>
+{% endif  %}
+
 {% endblock %}
 {% block main %}
     <div class="content">