feat(resizable): add duration prop and CSS variable for animation customization

- Add `duration` prop (default 400ms) to control animation speed
- Add `--resizable-easing` CSS variable for theme-level easing control
- Document Tailwind arbitrary property syntax for inline easing
- Bump version to 1.2.1

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: bob-obringer

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to `@neynar/ui` will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.2.1] - 2025-01-20
+
+### Added
+- **ResizablePanel**: Added `duration` prop (default 400ms) and `--resizable-easing` CSS variable for animation customization.
+
+---
+
 ## [1.2.0] - 2025-01-20
 
 ### Added

llm/components/resizable.llm.md

@@ -72,6 +72,7 @@ All panels inherit props from react-resizable-panels Panel component.
 | collapsedSize | number \| string | 0 | Size when collapsed |
 | collapsed | boolean | - | Controlled collapsed state. Panel syncs to this value. |
 | animated | boolean | false | Enable smooth CSS transition for collapse/expand. Drag resizing stays instant. |
+| duration | number | 400 | Animation duration in milliseconds. Only applies when `animated` is true. |
 | onResize | (size: { asPercentage: number; inPixels: number }) => void | - | Called when panel is resized |
 | onCollapse | () => void | - | Called when panel collapses |
 | onExpand | () => void | - | Called when panel expands |
@@ -230,6 +231,22 @@ function MonitoredPanels() {
 
 Use `collapsed` prop for declarative control and `animated` for smooth transitions. Drag resizing remains instant (no animation lag).
 
+**Customization:**
+- `duration` prop controls speed (default 400ms)
+- `--resizable-easing` CSS variable controls easing curve (default `cubic-bezier(0.16, 1, 0.3, 1)`)
+
+```tsx
+// Custom duration
+<ResizablePanel animated duration={200} collapsed={isCollapsed} />
+
+// Custom easing via Tailwind arbitrary property
+<ResizablePanel
+  className="[--resizable-easing:ease-out]"
+  animated
+  collapsed={isCollapsed}
+/>
+```
+
 ```tsx
 import { useState } from "react"
 import {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@neynar/ui",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "license": "MIT",
   "author": "Neynar Inc.",
   "description": "AI-first React component library for coding agents. LLM-optimized docs, sensible defaults, zero config. Built on shadcn patterns, Base UI, and Tailwind CSS v4.",

src/components/ui/resizable.tsx

@@ -10,13 +10,17 @@ import {
 
 import { cn } from "@/lib/utils";
 
-/** Duration of the collapse/expand animation in milliseconds. */
-const TRANSITION_DURATION = 300;
+/** Default duration of the collapse/expand animation in milliseconds. */
+const DEFAULT_DURATION = 400;
 
-/** CSS transition value for animated collapse/expand. */
-const TRANSITION_STYLE =
-  "flex-grow 0.3s cubic-bezier(0.16, 1, 0.3, 1), flex-basis 0.3s cubic-bezier(0.16, 1, 0.3, 1)";
+/** Default easing function for collapse/expand animations. */
+const DEFAULT_EASING = "cubic-bezier(0.16, 1, 0.3, 1)";
 
+/** Generate CSS transition value for animated collapse/expand. */
+function getTransitionStyle(durationMs: number, easing: string): string {
+  const seconds = durationMs / 1000;
+  return `flex-grow ${seconds}s ${easing}, flex-basis ${seconds}s ${easing}`;
+}
 
 type ResizablePanelGroupProps = React.ComponentProps<typeof PanelGroup>;
 
@@ -48,6 +52,8 @@ type ResizablePanelProps = Omit<
   animated?: boolean;
   /** Controlled collapsed state. When provided, the panel syncs to this value. */
   collapsed?: boolean;
+  /** Animation duration in milliseconds. Only applies when `animated` is true. @default 400 */
+  duration?: number;
 };
 
 /**
@@ -64,17 +70,20 @@ function ResizablePanel({
   className,
   animated,
   collapsed,
+  duration = DEFAULT_DURATION,
   ...props
 }: ResizablePanelProps) {
   const panelRef = React.useRef<PanelImperativeHandle>(null);
   const elementRef = React.useRef<HTMLDivElement>(null);
   const animatedRef = React.useRef(animated);
+  const durationRef = React.useRef(duration);
   const isFirstRender = React.useRef(true);
 
-  // Keep the ref in sync with prop changes
+  // Keep the refs in sync with prop changes
   React.useEffect(() => {
     animatedRef.current = animated;
-  }, [animated]);
+    durationRef.current = duration;
+  }, [animated, duration]);
 
   /** Apply transition, call action, then remove transition after duration */
   const withTransition = React.useCallback(
@@ -84,11 +93,17 @@ function ResizablePanel({
       ) as HTMLElement | null;
 
       if (animatedRef.current && panelEl && !skipAnimation) {
-        panelEl.style.transition = TRANSITION_STYLE;
+        const ms = durationRef.current;
+        // Read easing from CSS variable, fallback to default
+        const easing =
+          getComputedStyle(panelEl)
+            .getPropertyValue("--resizable-easing")
+            .trim() || DEFAULT_EASING;
+        panelEl.style.transition = getTransitionStyle(ms, easing);
         action();
         setTimeout(() => {
           panelEl.style.transition = "";
-        }, TRANSITION_DURATION);
+        }, ms);
       } else {
         action();
       }

src/styles/styles.css

@@ -73,6 +73,10 @@
   body {
     @apply font-sans bg-background text-foreground;
   }
+  :root {
+    /* Resizable panel animation easing - override in theme or component */
+    --resizable-easing: cubic-bezier(0.16, 1, 0.3, 1);
+  }
 }
 
 /* Surface blur effect - value comes from theme's --surface-blur variable */