feat: add theme support and refactor assets

Introduce support for themes by adding a `theme` parameter to the site generation process and as an argument to the main script. Created separate CSS files for different themes and adjusted the structure to accommodate the style changes. Also, updated the use of assets with new SVG images and logos.

Refactored HTML templates to dynamically select the theme and updated path references to images accordingly. Improved the development experience by adding a default "plain" theme and enhancing command-line argument parsing for theme selection.

Closes #7

main.py

@@ -56,16 +56,18 @@ def render_template_to_file(template_name, output_name, **kwargs):
     try:
         template = env.get_template(template_name)
         output_path = output_dir / output_name
+        kwargs.setdefault("theme", "plain")
         with open(output_path, "w", encoding="utf-8") as f:
             f.write(template.render(**kwargs))
     except TemplateNotFound:
         print(f"Template {template_name} not found.")
 
 
-def generate_static_site(development_mode=False):
+def generate_static_site(development_mode=False, theme="plain"):
     # Common context
     kwargs = {
         "timestamp": int(datetime.datetime.now().timestamp()),
+        "theme": theme,
     }
 
     if development_mode:
@@ -171,10 +173,13 @@ if __name__ == "__main__":
     parser.add_argument(
         "--port", type=int, default=8000, help="Port to serve the site on"
     )
+    parser.add_argument(
+        "--theme", type=str, default="plain", help="Theme to use for the site"
+    )
 
     args = parser.parse_args()
 
-    generate_static_site(development_mode=args.dev)
+    generate_static_site(development_mode=args.dev, theme=args.theme)
 
     if args.serve:
         server = TCPServer(("", args.port), StaticPageHandler)