diff --git a/shared/infrastructure/factory.py b/shared/infrastructure/factory.py
index 55d8c51..9512277 100644
--- a/shared/infrastructure/factory.py
+++ b/shared/infrastructure/factory.py
@@ -49,6 +49,7 @@ def create_base_app(
     domain_services_fn: Callable[[], None] | None = None,
     no_oauth: bool = False,
     no_db: bool = False,
+    css_extras: Sequence[str] | None = None,
 ) -> Quart:
     """
     Create a Quart app with shared infrastructure.
@@ -139,17 +140,24 @@ def create_base_app(
     _styles = BASE_DIR / "static" / "styles"
     _fa_css = BASE_DIR / "static" / "fontawesome" / "css"
     if (_styles / "tw.css").exists() and not registry_loaded():
-        load_css_registry(
-            _styles / "tw.css",
-            extra_css=[
+        if css_extras is None:
+            # Legacy default: all shared CSS for blog/market/etc apps
+            _extra = [
                 _styles / "basics.css",
                 _styles / "cards.css",
                 _styles / "blog-content.css",
                 _styles / "prism.css",
                 _fa_css / "all.min.css",
                 _fa_css / "v4-shims.min.css",
-            ],
-            url_rewrites={"../webfonts/": "/static/fontawesome/webfonts/"},
+            ]
+            _rewrites = {"../webfonts/": "/static/fontawesome/webfonts/"}
+        else:
+            _extra = [_styles / e if "/" not in e else e for e in css_extras]
+            _rewrites = {}
+        load_css_registry(
+            _styles / "tw.css",
+            extra_css=_extra,
+            url_rewrites=_rewrites,
         )
 
     # Dev-mode: auto-reload sx templates when files change on disk
diff --git a/sx/app.py b/sx/app.py
index 6499893..e1f51ed 100644
--- a/sx/app.py
+++ b/sx/app.py
@@ -64,6 +64,7 @@ def create_app() -> "Quart":
         "sx",
         context_fn=sx_standalone_context if SX_STANDALONE else sx_docs_context,
         domain_services_fn=register_domain_services,
+        css_extras=[],  # No legacy CSS — SX uses CSSX + custom highlighting
         **extra_kw,
     )