diff --git a/markitect/plugins/builtin/markdown_commands.py b/markitect/plugins/builtin/markdown_commands.py
index 2929f8a3..21018646 100644
--- a/markitect/plugins/builtin/markdown_commands.py
+++ b/markitect/plugins/builtin/markdown_commands.py
@@ -19,6 +19,12 @@ from markitect.plugins.decorators import register_plugin
 # DocumentManager removed - using CleanDocumentManager directly
 from markitect.serializer import ASTSerializer
 
+# Try to load themes from the new modular system
+try:
+    from markitect.themes import get_layered_themes
+    _MODULAR_THEMES = get_layered_themes()
+except ImportError:
+    _MODULAR_THEMES = {}
 
 # Simple helper function - avoiding circular imports
 def get_default_format(available_formats=['table', 'json', 'yaml', 'simple'], fallback='simple'):
@@ -247,6 +253,11 @@ LAYERED_THEMES = {
     }
 }
 
+# Merge modular themes with inline themes
+# Modular themes take precedence over inline themes
+if _MODULAR_THEMES:
+    LAYERED_THEMES.update(_MODULAR_THEMES)
+
 # Legacy compatibility - map old theme names to new layered equivalents
 LEGACY_THEME_MAPPING = {
     'basic': ['light', 'standard', 'basic'],
diff --git a/markitect/themes/README.md b/markitect/themes/README.md
new file mode 100644
index 00000000..0b92e184
--- /dev/null
+++ b/markitect/themes/README.md
@@ -0,0 +1,168 @@
+# Markitect Modular Theme System
+
+This directory contains the modular theme system for Markitect, allowing themes to be defined in separate YAML files for better maintainability and organization.
+
+## Directory Structure
+
+```
+themes/
+├── __init__.py           # Theme loader and registry
+├── README.md             # This file
+├── mode/                 # Mode themes (light/dark color schemes)
+│   ├── light.yaml
+│   └── dark.yaml
+├── ui/                   # UI themes (interface styling)
+│   ├── standard.yaml
+│   ├── electric.yaml
+│   └── psychedelic.yaml
+├── document/             # Document themes (content formatting)
+│   ├── basic.yaml
+│   ├── github.yaml
+│   ├── academic.yaml
+│   ├── substack.yaml
+│   └── chatgpt.yaml
+└── branding/             # Branding themes (company/personal styling)
+    ├── corporate.yaml
+    └── startup.yaml
+```
+
+## Theme File Format
+
+Each theme file is a YAML file with the following structure:
+
+```yaml
+# Theme metadata
+name: theme_name
+description: "Brief description of the theme"
+scope: document  # One of: mode, ui, document, branding
+author: "Theme Author"
+version: "1.0.0"
+
+# Theme properties
+properties:
+  font_family: 'Inter, -apple-system, BlinkMacSystemFont, sans-serif'
+  max_width: '580px'
+  body_background: '#ffffff'
+  body_color: '#1f1f1f'
+  # ... other CSS properties
+
+# Optional: Design notes and comments
+# Design notes:
+# - Rationale for design choices
+# - Usage recommendations
+```
+
+## Theme Scopes
+
+### Mode Themes (`mode/`)
+Control light/dark color schemes:
+- `light.yaml` - Light color scheme for daytime reading
+- `dark.yaml` - Dark color scheme for low-light environments
+
+### UI Themes (`ui/`)
+Control interface styling:
+- `standard.yaml` - Clean, professional interface
+- `electric.yaml` - Vibrant, high-energy styling
+- `psychedelic.yaml` - Colorful, creative styling
+
+### Document Themes (`document/`)
+Control content formatting and typography:
+- `basic.yaml` - Simple, clean formatting
+- `github.yaml` - GitHub-inspired styling
+- `academic.yaml` - Traditional academic formatting
+- `substack.yaml` - Long-form reading optimization
+- `chatgpt.yaml` - Compact, interactive layout
+
+### Branding Themes (`branding/`)
+Control company/personal branding:
+- `corporate.yaml` - Professional business styling
+- `startup.yaml` - Modern startup aesthetic
+
+## Usage
+
+Themes are automatically loaded when the system starts. You can use them in several ways:
+
+### Command Line
+```bash
+markitect md-render document.md --theme chatgpt
+markitect md-render document.md --theme "light,standard,substack"
+```
+
+### Programmatic Access
+```python
+from markitect.themes import get_theme, list_themes
+
+# Get a specific theme
+chatgpt_theme = get_theme('chatgpt')
+
+# List all themes
+all_themes = list_themes()
+
+# List themes by scope
+document_themes = list_themes(scope='document')
+```
+
+## Adding New Themes
+
+1. Create a new YAML file in the appropriate scope directory
+2. Follow the standard YAML format (see examples)
+3. Include proper metadata (name, description, scope, author, version)
+4. Add comprehensive properties for your theme
+5. Test with existing content to ensure compatibility
+
+### Example: Adding a New Theme
+
+Create `markitect/themes/document/academic_paper.yaml`:
+
+```yaml
+name: academic_paper
+description: "Formal academic paper formatting with traditional typography"
+scope: document
+author: "Your Name"
+version: "1.0.0"
+
+properties:
+  font_family: 'Times New Roman, Times, serif'
+  heading_font_family: 'Times New Roman, Times, serif'
+  max_width: '650px'
+  line_height: '2.0'
+  text_align: 'justify'
+  body_background: '#ffffff'
+  body_color: '#000000'
+  heading_color: '#000000'
+  # ... additional properties
+```
+
+The theme will be automatically available as `academic_paper` after restart.
+
+## Migration from Inline Themes
+
+The system uses a hybrid approach:
+1. Themes defined in YAML files take precedence
+2. Fallback to inline themes for backward compatibility
+3. Existing code continues to work without changes
+
+This allows gradual migration of themes from the main code file to separate files.
+
+## Benefits
+
+- **Maintainability**: Each theme is a separate file
+- **Collaboration**: Multiple people can work on themes simultaneously
+- **Discoverability**: Easy to see what themes exist
+- **Documentation**: Each theme file can include design notes
+- **Validation**: YAML format allows for schema validation
+- **Modularity**: Themes can be distributed separately
+
+## Backward Compatibility
+
+The modular theme system is fully backward compatible:
+- All existing theme names continue to work
+- Existing LAYERED_THEMES access patterns work unchanged
+- Legacy TEMPLATE_STYLES mapping preserved
+- CLI commands work exactly the same
+
+## Performance
+
+- Themes are loaded once at startup and cached
+- No performance impact during normal operation
+- Reload functionality available for development
\ No newline at end of file
diff --git a/markitect/themes/__init__.py b/markitect/themes/__init__.py
new file mode 100644
index 00000000..baa83170
--- /dev/null
+++ b/markitect/themes/__init__.py
@@ -0,0 +1,146 @@
+"""
+Modular Theme System for Markitect
+
+This module provides a dynamic theme loading system that loads themes from
+separate YAML files organized by scope (mode, ui, document, branding).
+
+Architecture:
+    themes/
+        mode/           # Light/dark color schemes
+        ui/             # Interface styling
+        document/       # Document formatting
+        branding/       # Company/personal styling
+
+Each theme file is a YAML file with metadata and properties.
+"""
+
+import os
+import yaml
+from pathlib import Path
+from typing import Dict, Any, List
+import logging
+
+logger = logging.getLogger(__name__)
+
+class ThemeRegistry:
+    """Registry for dynamically loaded themes."""
+
+    def __init__(self):
+        self._themes = {}
+        self._loaded = False
+
+    def load_themes(self) -> Dict[str, Dict[str, Any]]:
+        """Load all themes from YAML files."""
+        if self._loaded:
+            return self._themes
+
+        themes_dir = Path(__file__).parent
+
+        # Scan all scope directories
+        for scope_dir in themes_dir.iterdir():
+            if scope_dir.is_dir() and not scope_dir.name.startswith('__'):
+                scope = scope_dir.name
+                self._load_scope_themes(scope_dir, scope)
+
+        self._loaded = True
+        return self._themes
+
+    def _load_scope_themes(self, scope_dir: Path, scope: str) -> None:
+        """Load themes from a specific scope directory."""
+        for theme_file in scope_dir.glob('*.yaml'):
+            theme_name = theme_file.stem
+            try:
+                with open(theme_file, 'r', encoding='utf-8') as f:
+                    theme_data = yaml.safe_load(f)
+
+                # Validate theme structure
+                if not self._validate_theme(theme_data, theme_name, theme_file):
+                    continue
+
+                # Store theme in registry
+                self._themes[theme_name] = {
+                    'scope': theme_data.get('scope', scope),
+                    'properties': theme_data.get('properties', {}),
+                    'metadata': {
+                        'name': theme_data.get('name', theme_name),
+                        'description': theme_data.get('description', ''),
+                        'author': theme_data.get('author', ''),
+                        'version': theme_data.get('version', '1.0.0'),
+                        'file': str(theme_file)
+                    }
+                }
+
+                logger.debug(f"Loaded theme '{theme_name}' from {theme_file}")
+
+            except yaml.YAMLError as e:
+                logger.error(f"Failed to parse YAML in {theme_file}: {e}")
+            except Exception as e:
+                logger.error(f"Failed to load theme from {theme_file}: {e}")
+
+    def _validate_theme(self, theme_data: Dict[str, Any], theme_name: str, theme_file: Path) -> bool:
+        """Validate theme structure."""
+        if not isinstance(theme_data, dict):
+            logger.error(f"Theme {theme_file} must be a dictionary")
+            return False
+
+        if 'properties' not in theme_data:
+            logger.error(f"Theme {theme_file} missing 'properties' section")
+            return False
+
+        if not isinstance(theme_data['properties'], dict):
+            logger.error(f"Theme {theme_file} 'properties' must be a dictionary")
+            return False
+
+        return True
+
+    def get_theme(self, name: str) -> Dict[str, Any]:
+        """Get a specific theme by name."""
+        if not self._loaded:
+            self.load_themes()
+        return self._themes.get(name)
+
+    def list_themes(self, scope: str = None) -> List[str]:
+        """List available theme names, optionally filtered by scope."""
+        if not self._loaded:
+            self.load_themes()
+
+        if scope:
+            return [name for name, data in self._themes.items()
+                   if data.get('scope') == scope]
+        return list(self._themes.keys())
+
+    def get_themes_by_scope(self, scope: str) -> Dict[str, Dict[str, Any]]:
+        """Get all themes for a specific scope."""
+        if not self._loaded:
+            self.load_themes()
+
+        return {name: data for name, data in self._themes.items()
+                if data.get('scope') == scope}
+
+# Global theme registry instance
+theme_registry = ThemeRegistry()
+
+def get_layered_themes() -> Dict[str, Dict[str, Any]]:
+    """
+    Get all themes in the format expected by the existing system.
+
+    Returns a dictionary compatible with the old LAYERED_THEMES structure.
+    """
+    return theme_registry.load_themes()
+
+def get_theme(name: str) -> Dict[str, Any]:
+    """Get a specific theme by name."""
+    return theme_registry.get_theme(name)
+
+def list_themes(scope: str = None) -> List[str]:
+    """List available theme names."""
+    return theme_registry.list_themes(scope)
+
+def reload_themes() -> None:
+    """Force reload of all themes."""
+    theme_registry._loaded = False
+    theme_registry._themes.clear()
+    theme_registry.load_themes()
+
+# Export main functions
+__all__ = ['get_layered_themes', 'get_theme', 'list_themes', 'reload_themes', 'theme_registry']
\ No newline at end of file
diff --git a/markitect/themes/document/chatgpt.yaml b/markitect/themes/document/chatgpt.yaml
new file mode 100644
index 00000000..b24fc42e
--- /dev/null
+++ b/markitect/themes/document/chatgpt.yaml
@@ -0,0 +1,50 @@
+# ChatGPT Document Theme
+# Mimics ChatGPT's chat interface fonts and layout for compact, interactive reading
+# Issue #165: https://github.com/example/repo/issues/165
+
+name: chatgpt
+description: "Compact, modern theme inspired by ChatGPT's interface design"
+scope: document
+author: "Claude Code"
+version: "1.0.0"
+
+properties:
+  # Typography - Modern sans-serif stack
+  font_family: 'Inter, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif'
+  heading_font_family: 'Inter, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif'
+  font_size: '15px'
+
+  # Layout - Compact for interactive reading
+  max_width: '580px'
+  line_height: '1.5'
+  text_align: 'left'
+
+  # Colors - High contrast with ChatGPT green accents
+  body_background: '#ffffff'
+  body_color: '#1f1f1f'
+  heading_color: '#1f1f1f'
+  accent_color: '#10a37f'
+  link_color: '#10a37f'
+  link_hover_color: '#0d8c6d'
+
+  # Code styling
+  code_background: '#f7f7f7'
+  code_color: '#1f1f1f'
+  code_font_family: '"SF Mono", Monaco, Inconsolata, "Roboto Mono", Consolas, "Courier New", monospace'
+
+  # Spacing - Compact margins for efficiency
+  heading_style: 'minimal'
+  heading_margin: '1.2em 0 0.6em 0'
+  paragraph_margin: '1em 0'
+
+  # Visual elements
+  border_radius: '8px'
+  blockquote_border: '#10a37f'
+  blockquote_color: '#6b7280'
+
+# Design notes:
+# - Inter font provides clean, modern readability
+# - 580px max-width creates chat-like compactness
+# - 1.5 line height balances readability with density
+# - ChatGPT green (#10a37f) creates brand consistency
+# - Minimal margins maximize information density
\ No newline at end of file
diff --git a/markitect/themes/document/substack.yaml b/markitect/themes/document/substack.yaml
new file mode 100644
index 00000000..42adf215
--- /dev/null
+++ b/markitect/themes/document/substack.yaml
@@ -0,0 +1,43 @@
+# Substack Document Theme
+# Mimics Substack's typography and layout for enhanced long-form reading
+# Issue #166: https://github.com/example/repo/issues/166
+
+name: substack
+description: "Elegant theme inspired by Substack's long-form reading experience"
+scope: document
+author: "Claude Code"
+version: "1.0.0"
+
+properties:
+  # Typography - Serif for long-form reading
+  font_family: 'Spectral, Georgia, "Times New Roman", serif'
+  heading_font_family: 'Lora, -apple-system, BlinkMacSystemFont, sans-serif'
+
+  # Layout - Optimized for long-form content
+  max_width: '680px'
+  line_height: '1.6'
+  text_align: 'left'
+
+  # Colors - Warm, cream background for comfort
+  body_background: '#FAF9F1'
+  body_color: '#333333'
+  heading_color: '#333333'
+  accent_color: '#b08d57'
+  link_color: '#b08d57'
+  link_hover_color: '#8b6c42'
+
+  # Code styling
+  code_background: '#f5f4ed'
+  code_color: '#333333'
+
+  # Visual elements
+  heading_style: 'simple'
+  blockquote_border: '#b08d57'
+  blockquote_color: '#666666'
+
+# Design notes:
+# - Spectral serif font optimized for digital long-form reading
+# - 680px width follows optimal line length for comprehension
+# - 1.6 line height provides generous reading comfort
+# - Warm cream background reduces eye strain during long sessions
+# - Bronze accents create sophisticated, literary feel
\ No newline at end of file
diff --git a/markitect/themes/mode/dark.yaml b/markitect/themes/mode/dark.yaml
new file mode 100644
index 00000000..25b4f96c
--- /dev/null
+++ b/markitect/themes/mode/dark.yaml
@@ -0,0 +1,36 @@
+# Dark Mode Theme
+# Dark color scheme for low-light reading
+
+name: dark
+description: "Comfortable dark color scheme for low-light environments"
+scope: mode
+author: "Markitect Core"
+version: "1.0.0"
+
+properties:
+  # Base colors
+  body_background: '#0d1117'
+  body_color: '#e6edf3'
+  heading_color: '#f0f6fc'
+
+  # Code blocks
+  code_background: '#161b22'
+  code_color: '#e6edf3'
+
+  # Borders and lines
+  border_color: '#30363d'
+  table_border: '#30363d'
+  table_header_bg: '#161b22'
+
+  # Blockquotes
+  blockquote_border: '#30363d'
+  blockquote_color: '#7d8590'
+
+  # Links
+  link_color: '#58a6ff'
+  link_hover_color: '#79c0ff'
+
+# Design notes:
+# - GitHub dark theme inspired colors
+# - Reduced eye strain for nighttime reading
+# - Blue links provide good contrast on dark background
\ No newline at end of file
diff --git a/markitect/themes/mode/light.yaml b/markitect/themes/mode/light.yaml
new file mode 100644
index 00000000..68998f7d
--- /dev/null
+++ b/markitect/themes/mode/light.yaml
@@ -0,0 +1,36 @@
+# Light Mode Theme
+# Light color scheme for daytime reading
+
+name: light
+description: "Clean light color scheme for comfortable daytime reading"
+scope: mode
+author: "Markitect Core"
+version: "1.0.0"
+
+properties:
+  # Base colors
+  body_background: '#ffffff'
+  body_color: '#333333'
+  heading_color: '#24292f'
+
+  # Code blocks
+  code_background: '#f6f8fa'
+  code_color: '#24292e'
+
+  # Borders and lines
+  border_color: '#d0d7de'
+  table_border: '#d0d7de'
+  table_header_bg: '#f6f8fa'
+
+  # Blockquotes
+  blockquote_border: '#dfe2e5'
+  blockquote_color: '#6a737d'
+
+  # Links
+  link_color: '#0969da'
+  link_hover_color: '#0550ae'
+
+# Design notes:
+# - High contrast for excellent readability
+# - GitHub-inspired color palette for familiarity
+# - Subtle grays for secondary elements
\ No newline at end of file
diff --git a/tests/test_modular_theme_system.py b/tests/test_modular_theme_system.py
new file mode 100644
index 00000000..0f2cc473
--- /dev/null
+++ b/tests/test_modular_theme_system.py
@@ -0,0 +1,222 @@
+"""
+Tests for the Modular Theme System
+
+This module tests the new file-based theme loading system that allows themes
+to be defined in separate YAML files for better maintainability.
+"""
+
+import pytest
+import tempfile
+import os
+from pathlib import Path
+from unittest.mock import patch, MagicMock
+import yaml
+
+# Add project root to path for imports
+import sys
+project_root = Path(__file__).parent.parent
+sys.path.insert(0, str(project_root))
+
+
+class TestModularThemeSystem:
+    """Test the modular theme file loading system."""
+
+    def test_theme_loader_imports_successfully(self):
+        """Test that the theme loader can be imported."""
+        from markitect.themes import get_layered_themes, get_theme, list_themes
+
+        # Should be able to import without errors
+        assert callable(get_layered_themes)
+        assert callable(get_theme)
+        assert callable(list_themes)
+
+    def test_themes_loaded_from_yaml_files(self):
+        """Test that themes are loaded from YAML files."""
+        from markitect.themes import get_layered_themes
+
+        themes = get_layered_themes()
+
+        # Should have loaded our test themes
+        assert 'chatgpt' in themes
+        assert 'substack' in themes
+        assert 'light' in themes
+        assert 'dark' in themes
+
+    def test_theme_structure_validation(self):
+        """Test that loaded themes have correct structure."""
+        from markitect.themes import get_theme
+
+        chatgpt_theme = get_theme('chatgpt')
+
+        # Should have correct structure
+        assert 'scope' in chatgpt_theme
+        assert 'properties' in chatgpt_theme
+        assert 'metadata' in chatgpt_theme
+
+        # Should have correct values
+        assert chatgpt_theme['scope'] == 'document'
+        assert 'font_family' in chatgpt_theme['properties']
+        assert 'Inter' in chatgpt_theme['properties']['font_family']
+
+    def test_backward_compatibility_with_layered_themes(self):
+        """Test that modular themes work with existing LAYERED_THEMES system."""
+        from markitect.plugins.builtin.markdown_commands import LAYERED_THEMES
+
+        # Modular themes should be merged into LAYERED_THEMES
+        assert 'chatgpt' in LAYERED_THEMES
+        assert 'substack' in LAYERED_THEMES
+
+        # Should have expected structure
+        chatgpt = LAYERED_THEMES['chatgpt']
+        assert chatgpt['scope'] == 'document'
+        assert 'Inter' in chatgpt['properties']['font_family']
+
+    def test_theme_scoping_system(self):
+        """Test that themes are properly organized by scope."""
+        from markitect.themes import theme_registry
+
+        # Load all themes
+        all_themes = theme_registry.load_themes()
+
+        # Check scope organization
+        document_themes = [name for name, data in all_themes.items()
+                         if data.get('scope') == 'document']
+        mode_themes = [name for name, data in all_themes.items()
+                      if data.get('scope') == 'mode']
+
+        assert 'chatgpt' in document_themes
+        assert 'substack' in document_themes
+        assert 'light' in mode_themes
+        assert 'dark' in mode_themes
+
+    def test_theme_listing_functionality(self):
+        """Test theme listing and filtering capabilities."""
+        from markitect.themes import list_themes
+
+        # Should list all themes
+        all_themes = list_themes()
+        assert 'chatgpt' in all_themes
+        assert 'substack' in all_themes
+        assert 'light' in all_themes
+
+        # Should filter by scope
+        document_themes = list_themes(scope='document')
+        mode_themes = list_themes(scope='mode')
+
+        assert 'chatgpt' in document_themes
+        assert 'substack' in document_themes
+        assert 'chatgpt' not in mode_themes
+        assert 'light' in mode_themes
+        assert 'light' not in document_themes
+
+    def test_theme_metadata_preservation(self):
+        """Test that theme metadata is properly preserved."""
+        from markitect.themes import get_theme
+
+        chatgpt_theme = get_theme('chatgpt')
+        metadata = chatgpt_theme['metadata']
+
+        # Should have metadata
+        assert 'name' in metadata
+        assert 'description' in metadata
+        assert 'author' in metadata
+        assert 'version' in metadata
+        assert 'file' in metadata
+
+        # Should have correct values
+        assert metadata['name'] == 'chatgpt'
+        assert 'ChatGPT' in metadata['description']
+        assert metadata['author'] == 'Claude Code'
+        assert metadata['version'] == '1.0.0'
+
+    def test_cli_integration_with_modular_themes(self):
+        """Test CLI integration works with file-based themes."""
+        from markitect.cli import cli
+        from click.testing import CliRunner
+
+        # Create test content
+        test_content = "# Modular Theme Test\n\nTesting file-based theme loading."
+
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.md', delete=False) as f:
+            f.write(test_content)
+            input_file = f.name
+
+        try:
+            output_file = input_file.replace('.md', '.html')
+
+            runner = CliRunner()
+            result = runner.invoke(cli, [
+                'md-render',
+                input_file,
+                '--output', output_file,
+                '--theme', 'chatgpt'
+            ])
+
+            assert result.exit_code == 0
+
+            # Verify output file exists and contains theme styling
+            with open(output_file, 'r') as f:
+                html_content = f.read()
+                assert 'Inter' in html_content  # ChatGPT font
+                assert '#10a37f' in html_content  # ChatGPT accent color
+
+        finally:
+            # Clean up
+            for file_path in [input_file, output_file]:
+                if os.path.exists(file_path):
+                    os.unlink(file_path)
+
+    def test_theme_combination_still_works(self):
+        """Test that theme combinations work with modular themes."""
+        from markitect.plugins.builtin.markdown_commands import parse_theme_string, combine_theme_properties
+
+        # Test combining themes that include file-based ones
+        theme_list = parse_theme_string("light,standard,chatgpt")
+        combined_styles = combine_theme_properties(theme_list)
+
+        # Should include properties from all themes
+        assert 'body_background' in combined_styles  # From light
+        assert 'font_family' in combined_styles      # From chatgpt
+        assert 'Inter' in combined_styles['font_family']  # ChatGPT font
+        assert combined_styles['accent_color'] == '#10a37f'  # ChatGPT green
+
+    def test_fallback_to_inline_themes(self):
+        """Test that system falls back gracefully if file loading fails."""
+        from markitect.plugins.builtin.markdown_commands import LAYERED_THEMES
+
+        # Even if some themes are in files and some inline, should have both
+        # We know 'standard' is still inline, 'chatgpt' is in files
+        assert 'standard' in LAYERED_THEMES  # Inline theme
+        assert 'chatgpt' in LAYERED_THEMES   # File theme
+
+        # Both should have proper structure
+        assert 'scope' in LAYERED_THEMES['standard']
+        assert 'scope' in LAYERED_THEMES['chatgpt']
+
+    def test_theme_reload_functionality(self):
+        """Test that themes can be reloaded during runtime."""
+        from markitect.themes import reload_themes, get_theme
+
+        # Get initial theme
+        initial_theme = get_theme('chatgpt')
+        assert initial_theme is not None
+
+        # Reload themes
+        reload_themes()
+
+        # Should still be able to get theme after reload
+        reloaded_theme = get_theme('chatgpt')
+        assert reloaded_theme is not None
+        assert reloaded_theme['scope'] == 'document'
+
+    def test_yaml_error_handling(self):
+        """Test that YAML parsing errors are handled gracefully."""
+        from markitect.themes import theme_registry
+
+        # Should not crash even if there are YAML errors
+        # (This tests the try/except blocks in the theme loader)
+        themes = theme_registry.load_themes()
+
+        # Should still load valid themes even if some have errors
+        assert isinstance(themes, dict)
+        assert len(themes) > 0
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