Dynamically register which CSS files are needed.

src/context/src_block.rs

@@ -34,7 +34,7 @@ pub(crate) enum RenderSrcSegment {
     HighlightEnd,
 }
 
-render!(RenderSrcBlock, ISrcBlock, original, _render_context, {
+render!(RenderSrcBlock, ISrcBlock, original, render_context, {
     let lines = original
         .lines
         .iter()
@@ -55,6 +55,16 @@ render!(RenderSrcBlock, ISrcBlock, original, _render_context, {
             RenderSrcLine { children }
         })
         .collect();
+    match original.language.as_ref().map(String::as_str) {
+        Some("nix") => {
+            render_context
+                .dependency_manager
+                .lock()
+                .unwrap()
+                .include_css("language_nix.css")?;
+        }
+        _ => {}
+    };
     Ok(RenderSrcBlock {
         lines,
         language: original.language.clone(),