docs: enable edit links, custom styles, and extra markdown features on the site

Author: frostybee

docs/assets/css/custom.css

@@ -2,6 +2,7 @@ site:
   title: "Sarde"
   description: "Documentation for Sarde, a zero-config static site generator"
   url: "https://getsarde.github.io"
+  edit_url: "https://github.com/getsarde/sarde/edit/main/docs/content"
 
 build:
   # Project site at https://getsarde.github.io/sarde/
@@ -11,6 +12,22 @@ theme:
   name: "default"
   preset: "docs"
 
+head:
+  custom_css:
+  - css/custom.css
+
+markdown:
+  github_alerts: true
+  katex: true
+  mermaid: true
+  triple_colon_callouts: true
+  typographer: true
+  unsafe: false
+  codeblocks:
+    engine: nuri
+    light_theme: "github-light"
+    dark_theme: "github-dark-default"
+
 collections:
   docs:
     sort: "order"
@@ -35,7 +52,17 @@ plugins:
     - link_validator
     - redirects    
     - social_cards
+    - scroll-to-top
     - keyboard-nav
+  config:
+    scroll-to-top:
+      showProgressRing: true
+      showTooltip: true
+    keyboard-nav:
+      # Keep arrow-key navigation, drop the on-load hint toast and the
+      # chevron arrows pinned to the viewport edges.
+      show_hint: false
+      show_side_nav: true
 
 homepage:
   hero:
@@ -52,3 +79,17 @@ homepage:
       light: /images/hero-light.svg
       dark: /images/hero-dark.svg
       alt: "Hero illustration"
+social:
+- icon: github
+  label: GitHub
+  url: https://github.com/getsarde/sarde
+
+header:
+  links:
+  - label: Tags
+    url: /tags/  
+  - label: Changelog
+    url: /docs/changelog  
+  search: true
+  social: true
+  theme_toggle: true