feat: Implement dynamic style preview buttons

- Add JavaScript-based style copying from original elements to toolbar buttons
- Use getComputedStyle() to dynamically apply color, font-weight, text-decoration, text-transform
- Preserve button clickability with protected backgrounds and hover states
- Support any CSS framework/custom styles without hardcoded mappings
- Add comprehensive documentation to TODO.md for future enhancements

Examples:
- 'Emphasis' button now shows red bold text (from .emph class)
- 'Highlight' button displays with style preview while remaining clickable
- 'Brand' button demonstrates text-transform and color changes

This provides intuitive visual feedback so users immediately understand
what each formatting button will do to their content.

TODO.md

@@ -535,3 +535,125 @@ The HTTP server has been successfully implemented and is production-ready:
 **Priority**: Low - implement after core functionality is stable and enterprise customers request advanced permissions.
 
 **Design Principle**: Keep simple `.insertr-gate` as default, add optional complexity only when needed.
+
+## 🎨 **Style Preview Enhancement System** (Dec 2024)
+
+### **✅ IMPLEMENTED: Basic Style Button Previews**
+
+**Goal**: Make formatting buttons visually preview the styles they represent.
+
+**Current Implementation**:
+- ✅ **Dynamic Style Copying** - JavaScript reads computed styles from original elements
+- ✅ **Selective Property Application** - Copies color, font-weight, text-decoration, text-transform  
+- ✅ **Button Structure Preservation** - Maintains clickable button appearance with backgrounds/borders
+- ✅ **Cross-Platform Compatibility** - Uses `window.getComputedStyle()` for universal support
+
+**Example Results**:
+- "Emphasis" button displays with red bold text (from `.emph { color: #dc2626; font-weight: 700; }`)
+- "Highlight" button shows preview styling while remaining clickable
+- "Brand" button demonstrates text-transform and color changes
+
+### **🔄 Future Style Preview Enhancements**
+
+#### **🎯 Priority 1: Enhanced Style Support**
+- [ ] **Background Colors** - Safe background preview with contrast protection
+- [ ] **Border Styles** - Preview border styles while maintaining button structure  
+- [ ] **Typography Styles** - Font-family, font-size adjustments with readability limits
+- [ ] **Advanced CSS Properties** - Text-shadow, letter-spacing, line-height previews
+
+#### **🎯 Priority 2: Interactive Previews**
+- [ ] **Hover State Previews** - Show hover effects in button previews
+- [ ] **Animation Previews** - Preview CSS transitions and animations safely
+- [ ] **Responsive Previews** - Show how styles adapt across screen sizes
+- [ ] **Nested Style Previews** - Handle complex nested styling scenarios
+
+#### **🎯 Priority 3: Advanced Preview Features**  
+- [ ] **Custom Style Creation** - Visual style picker with live preview
+- [ ] **Style Inheritance Display** - Show which properties come from which classes
+- [ ] **Accessibility Validation** - Ensure previews meet contrast and readability standards
+- [ ] **Performance Optimization** - Cache computed styles, minimize recomputation
+
+### **🔧 Technical Implementation Details**
+
+**Current Approach** (JavaScript-based style copying):
+```javascript
+const computedStyle = window.getComputedStyle(styleInfo.element);
+if (computedStyle.color && computedStyle.color !== 'rgb(0, 0, 0)') {
+    button.style.setProperty('color', computedStyle.color, 'important');
+}
+```
+
+**Benefits**:
+- ✅ Works with any CSS framework or custom styles
+- ✅ No hardcoded style mappings required
+- ✅ Automatically adapts to theme changes
+- ✅ Handles complex CSS specificity scenarios
+
+**Limitations**:
+- ⚠️ Limited to properties safe for button elements
+- ⚠️ Background colors skipped to maintain readability
+- ⚠️ Some complex styles may not preview accurately
+- ⚠️ Performance impact on large style sets
+
+### **🎨 Design Considerations**
+
+**Readability vs Accuracy Trade-offs**:
+- **Button Backgrounds**: Always use safe background to ensure clickability
+- **Text Contrast**: Ensure sufficient contrast between text and button background
+- **Property Selection**: Only preview properties that don't break button functionality
+- **Fallback Handling**: Graceful degradation when style copying fails
+
+**User Experience Principles**:
+- **Immediate Recognition**: Users should instantly understand what each button does
+- **Consistent Interaction**: Buttons should always feel clickable regardless of style
+- **Visual Hierarchy**: Style previews shouldn't overpower the editor interface
+- **Accessibility**: Maintain WCAG compliance for all preview combinations
+
+### **🧪 Testing Strategy for Style Previews**
+
+**Cross-Browser Compatibility**:
+- Test `getComputedStyle()` behavior across major browsers
+- Validate CSS custom property support and inheritance
+- Check for inconsistencies in color space handling
+
+**Edge Case Handling**:
+- Very long class names or deeply nested selectors
+- Conflicting CSS properties from multiple stylesheets
+- High contrast or accessibility mode compatibility
+- Performance with large numbers of detected styles
+
+**Real-World Style Testing**:
+- Test with popular CSS frameworks (Tailwind, Bootstrap, Bulma)
+- Validate with complex design systems and component libraries
+- Check compatibility with CSS-in-JS solutions
+- Test with user-defined custom properties and themes
+
+### **📊 Future Metrics and Analytics**
+
+**Style Preview Usage Analytics**:
+- Track which style previews are most commonly used
+- Measure user engagement with preview vs non-preview buttons  
+- Identify styles that cause preview rendering issues
+- Monitor performance impact of style computation
+
+**User Experience Improvements**:
+- A/B test preview accuracy vs simplified representations
+- Test user comprehension of style previews vs text labels
+- Measure editing efficiency with vs without previews
+- Gather feedback on preview helpfulness for different user types
+
+### **Integration with Future Features**
+
+**Style Management System**:
+- Style preview integration with custom style creation tools
+- Preview integration with theme switching and dark mode
+- Connection to style documentation and design system integration
+- Preview role in collaborative editing and style consistency
+
+**Performance Optimization**:
+- Style preview caching for frequently used styles
+- Lazy loading of preview computation for off-screen elements
+- Optimization for mobile devices and slower browsers
+- Integration with build-time style optimization
+
+**Note**: Current implementation provides solid foundation for all future enhancements while maintaining the zero-configuration philosophy.

internal/content/assets/insertr.css

@@ -380,6 +380,56 @@ body:not(.insertr-edit-mode) .insertr-editing-hover::after {
     transform: translateY(1px);
 }
 
+/* Style preview buttons - styled dynamically via JavaScript */
+.insertr-style-btn.insertr-style-preview {
+    /* Preserve button structure */
+    background: var(--insertr-bg-primary) !important;
+    border: 1px solid var(--insertr-border-color) !important;
+    border-radius: var(--insertr-border-radius) !important;
+    padding: var(--insertr-spacing-xs) var(--insertr-spacing-sm) !important;
+    font-size: var(--insertr-font-size-sm) !important;
+    cursor: pointer !important;
+    transition: var(--insertr-transition) !important;
+    
+    /* Button layout */
+    min-height: 28px;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    
+    /* Ensure button remains clickable */
+    position: relative;
+    
+    /* Styles will be applied dynamically via JavaScript */
+}
+
+/* Add subtle background to preview buttons to ensure they remain clickable-looking */
+.insertr-style-btn.insertr-style-preview::before {
+    content: '';
+    position: absolute;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    background: var(--insertr-bg-primary);
+    opacity: 0.9;
+    border-radius: inherit;
+    z-index: -1;
+}
+
+/* Hover state for preview buttons */
+.insertr-style-btn.insertr-style-preview:hover {
+    background: var(--insertr-bg-secondary) !important;
+    border-color: var(--insertr-text-muted) !important;
+    transform: none !important;
+}
+
+/* Active state for preview buttons */
+.insertr-style-btn.insertr-style-preview:active {
+    background: var(--insertr-border-color) !important;
+    transform: translateY(1px) !important;
+}
+
 /* Editor components */
 .insertr-simple-editor,
 .insertr-rich-editor,

lib/src/styles/insertr.css

@@ -380,6 +380,56 @@ body:not(.insertr-edit-mode) .insertr-editing-hover::after {
     transform: translateY(1px);
 }
 
+/* Style preview buttons - styled dynamically via JavaScript */
+.insertr-style-btn.insertr-style-preview {
+    /* Preserve button structure */
+    background: var(--insertr-bg-primary) !important;
+    border: 1px solid var(--insertr-border-color) !important;
+    border-radius: var(--insertr-border-radius) !important;
+    padding: var(--insertr-spacing-xs) var(--insertr-spacing-sm) !important;
+    font-size: var(--insertr-font-size-sm) !important;
+    cursor: pointer !important;
+    transition: var(--insertr-transition) !important;
+    
+    /* Button layout */
+    min-height: 28px;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    
+    /* Ensure button remains clickable */
+    position: relative;
+    
+    /* Styles will be applied dynamically via JavaScript */
+}
+
+/* Add subtle background to preview buttons to ensure they remain clickable-looking */
+.insertr-style-btn.insertr-style-preview::before {
+    content: '';
+    position: absolute;
+    top: 0;
+    left: 0;
+    right: 0;
+    bottom: 0;
+    background: var(--insertr-bg-primary);
+    opacity: 0.9;
+    border-radius: inherit;
+    z-index: -1;
+}
+
+/* Hover state for preview buttons */
+.insertr-style-btn.insertr-style-preview:hover {
+    background: var(--insertr-bg-secondary) !important;
+    border-color: var(--insertr-text-muted) !important;
+    transform: none !important;
+}
+
+/* Active state for preview buttons */
+.insertr-style-btn.insertr-style-preview:active {
+    background: var(--insertr-border-color) !important;
+    transform: translateY(1px) !important;
+}
+
 /* Editor components */
 .insertr-simple-editor,
 .insertr-rich-editor,

lib/src/ui/style-aware-editor.js

@@ -246,6 +246,42 @@ export class StyleAwareEditor {
         button.title = `Apply ${styleInfo.name} style`;
         button.dataset.styleId = styleId;
         
+        // Apply preview styling by copying computed styles from the original element
+        if (styleInfo.element && styleInfo.classes && styleInfo.classes.length > 0) {
+            // Add the detected classes first
+            styleInfo.classes.forEach(className => {
+                button.classList.add(className);
+            });
+            
+            // Add special button class
+            button.classList.add('insertr-style-preview');
+            
+            // Copy specific style properties from the original element to ensure they show
+            const computedStyle = window.getComputedStyle(styleInfo.element);
+            
+            // Copy color (most important for visual preview)
+            if (computedStyle.color && computedStyle.color !== 'rgb(0, 0, 0)') {
+                button.style.setProperty('color', computedStyle.color, 'important');
+            }
+            
+            // Copy font-weight
+            if (computedStyle.fontWeight && computedStyle.fontWeight !== '400') {
+                button.style.setProperty('font-weight', computedStyle.fontWeight, 'important');
+            }
+            
+            // Copy text-decoration (for underlines, etc.)
+            if (computedStyle.textDecoration && computedStyle.textDecoration !== 'none') {
+                button.style.setProperty('text-decoration', computedStyle.textDecoration, 'important');
+            }
+            
+            // Copy text-transform (for uppercase, etc.)  
+            if (computedStyle.textTransform && computedStyle.textTransform !== 'none') {
+                button.style.setProperty('text-transform', computedStyle.textTransform, 'important');
+            }
+            
+            // Don't copy background-color to keep button appearance
+        }
+        
         // Add click handler for style application
         button.addEventListener('click', (e) => {
             e.preventDefault();