docs(themes): add syntax highlighting documentation and test coverage

- Update syntax-highlighting.md with tree-house integration details
- Add themes/README.md explaining copy-to-project workflow
- Add 13 tests: hierarchical scopes, injections (Nix+bash, MD, HTML)
- All 64 tests passing

docs/content/features/syntax-highlighting.md

@@ -1,10 +1,10 @@
 ---
 title: Syntax Highlighting
-description: Build-time code highlighting with Tree-sitter
+description: Build-time code highlighting with Tree-sitter and tree-house
 weight: 3
 ---
 
-sukr highlights code blocks at build time using Tree-sitter. No client-side JavaScript required.
+sukr highlights code blocks at build time using [tree-house](https://github.com/helix-editor/tree-house) (Helix editor's Tree-sitter integration). No client-side JavaScript required.
 
 ## Usage
 
@@ -150,37 +150,81 @@ int main() {
 ## How It Works
 
 1. During Markdown parsing, code blocks are intercepted
-2. Tree-sitter parses the code and generates a syntax tree
+2. tree-house parses the code and generates a syntax tree
-3. Spans are generated with semantic CSS classes
+3. Spans are generated with **hierarchical CSS classes** (e.g., `.hl-keyword-control-return`)
-4. All work happens at build time
+4. All work happens at build time—zero JavaScript in the browser
 
-## Styling
+## Theme System
 
-Highlighted code uses semantic CSS classes:
+sukr uses a **decoupled theme system** with CSS custom properties. Themes are separate CSS files that define colors for syntax highlighting classes.
+
+### Hierarchical Scopes
+
+Highlighting uses fine-grained scope classes with hierarchical fallback:
+
+| Scope Class                       | Description           |
+| --------------------------------- | --------------------- |
+| `.hl-keyword`                     | Generic keywords      |
+| `.hl-keyword-control`             | Control flow          |
+| `.hl-keyword-control-return`      | return/break/continue |
+| `.hl-function`                    | Function names        |
+| `.hl-function-builtin`            | Built-in functions    |
+| `.hl-type`                        | Type names            |
+| `.hl-variable`                    | Variables             |
+| `.hl-variable-parameter`          | Function parameters   |
+| `.hl-string`                      | String literals       |
+| `.hl-comment`                     | Comments              |
+| `.hl-comment-block-documentation` | Doc comments          |
+
+If a theme only defines `.hl-keyword`, it will apply to all keyword subtypes.
+
+### Using a Theme
+
+Themes are CSS files that define the color palette. Import a theme at the top of your stylesheet:
 
 ```css
-.keyword {
+@import "path/to/theme.css";
-  color: #ff79c6;
-}
-.string {
-  color: #f1fa8c;
-}
-.function {
-  color: #50fa7b;
-}
-.comment {
-  color: #6272a4;
-}
-.number {
-  color: #bd93f9;
-}
 ```
 
-The exact classes depend on the language grammar.
+sukr uses [lightningcss](https://lightningcss.dev/) which inlines `@import` rules at build time, producing a single bundled CSS file.
+
+### Available Themes
+
+sukr includes several themes in the `themes/` directory:
+
+- **default.css** — Dracula-inspired dark theme (batteries included)
+- **dracula.css** — Classic Dracula colors
+- **gruvbox.css** — Warm retro palette
+- **nord.css** — Cool arctic colors
+- **github_dark.css** — GitHub's dark mode
+- **github_light.css** — GitHub's light mode
+
+Copy the theme files to your project and import as shown above.
+
+### Theme Structure
+
+Themes use CSS custom properties for easy customization:
+
+```css
+:root {
+  --hl-keyword: #ff79c6;
+  --hl-string: #f1fa8c;
+  --hl-function: #50fa7b;
+  --hl-comment: #6272a4;
+}
+
+.hl-keyword {
+  color: var(--hl-keyword);
+}
+.hl-string {
+  color: var(--hl-string);
+}
+/* ... */
+```
 
 ## Injection Support
 
-Some languages support injection—highlighting embedded languages. For example, Bash inside Nix strings:
+Some languages support **injection**—highlighting embedded languages. For example, bash inside Nix strings:
 
 ```nix
 stdenv.mkDerivation {
@@ -193,6 +237,8 @@ stdenv.mkDerivation {
 
 Markdown also supports injection—code blocks inside markdown fences are highlighted with their respective languages.
 
+Languages with injection support: Bash, C, CSS, Go, HTML, JavaScript, Markdown, Nix, Python, Rust, TOML, TypeScript, YAML.
+
 ## Fallback
 
 Unknown languages fall back to plain `<code>` blocks without highlighting.

src/highlight.rs

@@ -712,4 +712,188 @@ mod tests {
 
         assert!(html.contains("pkgs"));
     }
+
+    // === Hierarchical Scope Tests ===
+
+    #[test]
+    fn test_scope_to_class_generates_hierarchical_names() {
+        // Verify the SCOPE_CLASSES static contains hierarchical class names
+        let classes = SCOPE_CLASSES.clone();
+
+        // Should have keyword hierarchy
+        assert!(classes.contains(&"hl-keyword"));
+        assert!(classes.contains(&"hl-keyword-control"));
+        assert!(classes.contains(&"hl-keyword-control-return"));
+
+        // Should have function hierarchy
+        assert!(classes.contains(&"hl-function"));
+        assert!(classes.contains(&"hl-function-builtin"));
+
+        // Should have comment hierarchy
+        assert!(classes.contains(&"hl-comment"));
+        assert!(classes.contains(&"hl-comment-block-documentation"));
+    }
+
+    #[test]
+    fn test_hierarchical_scope_resolution_fallback() {
+        // Direct match should work
+        let kw = resolve_scope("keyword");
+        assert!(kw.is_some());
+
+        // Hierarchical match should find parent
+        let kw_ctrl = resolve_scope("keyword.control");
+        assert!(kw_ctrl.is_some());
+
+        // Deeper hierarchy should find closest ancestor
+        let kw_ctrl_ret = resolve_scope("keyword.control.return");
+        assert!(kw_ctrl_ret.is_some());
+
+        // Completely unknown should return None
+        assert!(resolve_scope("nonexistent.scope.here").is_none());
+    }
+
+    #[test]
+    fn test_highlight_generates_hl_prefixed_classes() {
+        // Rust code that should produce keyword highlighting
+        let code = "fn main() { return 42; }";
+        let html = highlight_code(Language::Rust, code);
+
+        // Should contain hl-prefixed span classes
+        assert!(
+            html.contains("hl-"),
+            "Expected hl-prefixed classes in: {html}"
+        );
+    }
+
+    #[test]
+    fn test_highlight_rust_keywords() {
+        let code = "pub fn foo() -> Result<(), Error> { Ok(()) }";
+        let html = highlight_code(Language::Rust, code);
+
+        // Should contain span elements
+        assert!(html.contains("<span"));
+        // Should have keyword classes (fn, pub, etc.)
+        assert!(html.contains("hl-keyword") || html.contains("class="));
+    }
+
+    #[test]
+    fn test_highlight_python_function_definition() {
+        let code = "def greet(name: str) -> str:\n    return f'Hello, {name}'";
+        let html = highlight_code(Language::Python, code);
+
+        // Should contain the function name
+        assert!(html.contains("greet"));
+        // Should have span highlighting
+        assert!(html.contains("<span"));
+    }
+
+    // === Injection Tests ===
+
+    #[test]
+    fn test_injection_nix_with_bash() {
+        // Nix code with bash in multi-line strings (common pattern)
+        let code = r#"
+stdenv.mkDerivation {
+  buildPhase = ''
+    echo "Building..."
+    make -j$NIX_BUILD_CORES
+  '';
+}
+"#;
+        let html = highlight_code(Language::Nix, code);
+
+        // Should produce HTML output with the nix content
+        assert!(html.contains("stdenv"));
+        assert!(html.contains("mkDerivation"));
+        // The injection should be handled (even if bash isn't fully highlighted, should not error)
+        assert!(html.contains("echo"));
+    }
+
+    #[test]
+    fn test_injection_markdown_with_fenced_code() {
+        // Markdown with a fenced code block
+        let code = r#"# Header
+
+Here is some code:
+
+```rust
+fn main() {}
+```
+"#;
+        let html = highlight_code(Language::Markdown, code);
+
+        // Should handle the markdown content
+        assert!(html.contains("Header"));
+        // Fenced code block should be present (may have spans inside)
+        assert!(html.contains("fn") && html.contains("main"));
+    }
+
+    #[test]
+    fn test_injection_html_with_script() {
+        // HTML with embedded JavaScript
+        let code = r#"
+<!DOCTYPE html>
+<html>
+<head>
+  <script>
+    const x = 42;
+    console.log(x);
+  </script>
+</head>
+</html>
+"#;
+        let html = highlight_code(Language::Html, code);
+
+        // Should contain HTML structure
+        assert!(html.contains("html"));
+        assert!(html.contains("script"));
+        // JavaScript content should be present
+        assert!(html.contains("const"));
+    }
+
+    #[test]
+    fn test_injection_html_with_style() {
+        // HTML with embedded CSS
+        let code = r#"
+<html>
+<head>
+  <style>
+    .container { display: flex; }
+  </style>
+</head>
+</html>
+"#;
+        let html = highlight_code(Language::Html, code);
+
+        // Should handle CSS injection
+        assert!(html.contains("style"));
+        assert!(html.contains("container"));
+        assert!(html.contains("flex"));
+    }
+
+    // === Edge Cases ===
+
+    #[test]
+    fn test_empty_input() {
+        let html = highlight_code(Language::Rust, "");
+        // Empty input should produce minimal output
+        assert!(html.is_empty() || html.len() < 10);
+    }
+
+    #[test]
+    fn test_whitespace_only_input() {
+        let html = highlight_code(Language::Rust, "   \n\t\n  ");
+        // Whitespace should be preserved
+        assert!(html.contains(' ') || html.contains('\n'));
+    }
+
+    #[test]
+    fn test_special_characters_escaped() {
+        let code = r#"let x = "<script>alert('xss')</script>";"#;
+        let html = highlight_code(Language::Rust, code);
+
+        // HTML special chars should be escaped
+        assert!(!html.contains("<script>"));
+        assert!(html.contains("&lt;") || html.contains("script"));
+    }
 }

themes/README.md

@@ -0,0 +1,90 @@
+# Syntax Highlighting Themes
+
+This directory contains CSS themes for sukr's syntax highlighting system.
+
+## Available Themes
+
+| Theme              | Description                 |
+| ------------------ | --------------------------- |
+| `default.css`      | Dracula-inspired dark theme |
+| `dracula.css`      | Classic Dracula colors      |
+| `gruvbox.css`      | Warm retro palette          |
+| `nord.css`         | Cool arctic colors          |
+| `github_dark.css`  | GitHub's dark mode          |
+| `github_light.css` | GitHub's light mode         |
+
+## Usage
+
+1. **Copy a theme** to your project's static directory
+2. **Import it** in your main CSS file:
+
+```css
+@import "themes/default.css";
+```
+
+sukr uses [lightningcss](https://lightningcss.dev/) which bundles `@import` rules at build time—your final CSS will be a single minified file.
+
+## Customization
+
+Themes use CSS custom properties for easy customization. Override any variable in your own CSS:
+
+```css
+@import "themes/default.css";
+
+/* Override just the keyword color */
+:root {
+  --hl-keyword: #e879f9;
+}
+```
+
+### Core Variables
+
+All themes define these variables in `:root`:
+
+| Variable        | Description            |
+| --------------- | ---------------------- |
+| `--hl-keyword`  | Keywords, control flow |
+| `--hl-string`   | String literals        |
+| `--hl-function` | Function names         |
+| `--hl-comment`  | Comments               |
+| `--hl-type`     | Type names             |
+| `--hl-number`   | Numeric literals       |
+| `--hl-variable` | Variables              |
+| `--hl-operator` | Operators              |
+
+## Hierarchical Scopes
+
+sukr generates **hierarchical CSS classes** for fine-grained styling:
+
+```html
+<span class="hl-keyword-control-return">return</span>
+```
+
+Themes can style at any level of specificity:
+
+```css
+/* All keywords */
+.hl-keyword {
+  color: var(--hl-keyword);
+}
+
+/* Just control-flow keywords */
+.hl-keyword-control {
+  color: #ff79c6;
+}
+
+/* Just return/break/continue */
+.hl-keyword-control-return {
+  font-weight: bold;
+}
+```
+
+If a specific class isn't styled, highlighting falls back up the hierarchy.
+
+## Creating Custom Themes
+
+Start with `default.css` and modify the `:root` variables to create your own color scheme. The class rules reference these variables, so changing values updates the entire theme.
+
+## Note
+
+These themes are **not bundled into the sukr binary**—they're provided as starting points. Copy what you need to your project and customize to match your site's design.