docs: add Tailwind CSS and shadcn/ui integration guide (#851)

Add documentation section covering best practices for using
react-split-pane with Tailwind CSS and shadcn/ui, including
direct class usage, custom divider components, and CSS variable
overrides.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[email protected]>

Author: tomkp

README.md

@@ -339,6 +339,115 @@ A subtle single-pixel divider:
 }
 ```
 
+## Tailwind CSS & shadcn/ui
+
+React Split Pane works seamlessly with Tailwind CSS and shadcn/ui. The component uses plain CSS and inline styles (no CSS-in-JS), so there are no conflicts with utility-first frameworks.
+
+### Using Tailwind Classes
+
+Apply Tailwind classes directly via `className` props. Skip importing the default stylesheet for full Tailwind control:
+
+```tsx
+import { SplitPane, Pane } from 'react-split-pane';
+// Don't import 'react-split-pane/styles.css' if using Tailwind
+
+<SplitPane
+  className="h-screen w-full"
+  dividerClassName="bg-gray-200 hover:bg-gray-300 dark:bg-gray-700 dark:hover:bg-gray-600 transition-colors"
+>
+  <Pane defaultSize="300px" className="bg-white dark:bg-gray-900 p-4">
+    <Sidebar />
+  </Pane>
+  <Pane className="bg-gray-50 dark:bg-gray-800 p-4">
+    <MainContent />
+  </Pane>
+</SplitPane>
+```
+
+### shadcn/ui Integration
+
+Use shadcn's CSS variables and utilities for consistent theming:
+
+```tsx
+import { SplitPane, Pane } from 'react-split-pane';
+
+<SplitPane
+  className="h-full w-full"
+  dividerClassName="bg-border hover:bg-accent transition-colors"
+>
+  <Pane defaultSize="280px" className="bg-background border-r">
+    <Sidebar />
+  </Pane>
+  <Pane className="bg-muted/50">
+    <MainContent />
+  </Pane>
+</SplitPane>
+```
+
+### Custom Divider with shadcn
+
+Create a themed divider component using shadcn's `cn` utility:
+
+```tsx
+import { cn } from '@/lib/utils';
+import type { DividerProps } from 'react-split-pane';
+
+function ThemedDivider({ direction, isDragging, disabled, ...props }: DividerProps) {
+  return (
+    <div
+      className={cn(
+        'flex items-center justify-center transition-colors',
+        'bg-border hover:bg-accent focus:outline-none focus:ring-2 focus:ring-ring',
+        direction === 'horizontal'
+          ? 'w-1 cursor-col-resize'
+          : 'h-1 cursor-row-resize',
+        isDragging && 'bg-primary',
+        disabled && 'cursor-not-allowed opacity-50'
+      )}
+      {...props}
+    />
+  );
+}
+
+<SplitPane divider={ThemedDivider}>
+  <Pane>Left</Pane>
+  <Pane>Right</Pane>
+</SplitPane>
+```
+
+### CSS Variables with Tailwind
+
+Override the default CSS variables in your `globals.css` to match your Tailwind theme:
+
+```css
+/* globals.css */
+@layer base {
+  :root {
+    --split-pane-divider-size: 4px;
+    --split-pane-divider-color: theme('colors.gray.200');
+    --split-pane-divider-color-hover: theme('colors.gray.300');
+    --split-pane-focus-color: theme('colors.blue.500');
+  }
+
+  .dark {
+    --split-pane-divider-color: theme('colors.gray.700');
+    --split-pane-divider-color-hover: theme('colors.gray.600');
+  }
+}
+```
+
+Or with shadcn/ui CSS variables:
+
+```css
+@layer base {
+  :root {
+    --split-pane-divider-color: hsl(var(--border));
+    --split-pane-divider-color-hover: hsl(var(--accent));
+    --split-pane-focus-color: hsl(var(--ring));
+  }
+}
+```
+
 ## Migration from v0.1.x
 
 See [MIGRATION.md](./MIGRATION.md) for detailed migration guide.