fix(ui): replace native scrollbars with custom controls

docs/design.md

@@ -248,7 +248,9 @@ control blurs, which rings it on `:focus`: a click or ⌘↵ doesn't count as ke
 Every hover is the same faint brand tint: fills use `--pn-hover`, borders `--pn-hover-line`; never `--pn-muted`, the
 solid accent or a status color. Selected and active states keep their own fills (`--pn-accent-soft`,
 `--pn-nav-active`). Destructive colors identify actions at rest and validation errors; their hover is the same blue.
-Scrollable surfaces use thin, rounded scrollbars with the theme's line color on a transparent track, including portals.
+Converted scrollable surfaces use `CustomScrollbar`: a narrow, rounded thumb in the theme's line color on a transparent
+track, with pointer dragging, track clicks and keyboard navigation. Only those viewports hide native scrollbars;
+other scroll regions retain their native controls, including horizontal controls in zoomed PDF viewers.
 Chip overflow counts open a themed popover on hover or click, listing full names on separate lines without truncation;
 keyboard users open it with Enter or Space and dismiss it with Escape.
 Tooltips use the same raised surface, foreground, border and corner radius as overflow popovers. Both open below

src/components/primitives/avatar-group.tsx

@@ -1,3 +1,4 @@
+import { CustomScrollbar } from "@/components/primitives/custom-scrollbar"
 import { Avatar, AvatarFallback } from "@/components/ui/avatar"
 import { Popover, PopoverContent, PopoverTrigger } from "@/components/ui/popover"
 import { pluralize } from "@/lib/format"
@@ -80,7 +81,11 @@ export function AvatarGroup({ people, max = 7, listLabel = "Members", className
             <p className="border-b border-(--pn-line) px-3 py-2 text-xs text-(--pn-fg-muted) tabular-nums">
               {pluralize(rest.length, "more member")}
             </p>
-            <ul className="max-h-[min(20rem,var(--available-height))] overflow-y-auto overscroll-contain py-1">
+            <CustomScrollbar
+              as="ul"
+              className="max-h-[min(20rem,var(--available-height))]"
+              viewportClassName="overscroll-contain py-1"
+            >
               {rest.map((person) => (
                 <li key={person.id} className="flex h-9 items-center gap-2.5 px-3">
                   <PersonAvatar person={person} className="size-6 shrink-0" />
@@ -89,7 +94,7 @@ export function AvatarGroup({ people, max = 7, listLabel = "Members", className
                   </Hint>
                 </li>
               ))}
-            </ul>
+            </CustomScrollbar>
           </PopoverContent>
         </Popover>
       )}

src/components/primitives/chip-overflow.tsx

@@ -1,6 +1,7 @@
 import type * as React from "react"
 import { type ReactNode, useLayoutEffect, useRef, useState } from "react"
 
+import { CustomScrollbar } from "@/components/primitives/custom-scrollbar"
 import { Popover, PopoverContent, PopoverTitle, PopoverTrigger } from "@/components/ui/popover"
 import { cn } from "@/lib/utils"
 
@@ -121,14 +122,14 @@ export function ChipOverflow<T>({
             )}
           >
             <PopoverTitle className="sr-only">Additional items</PopoverTitle>
-            <ul className="flex max-h-72 flex-col gap-2 overflow-y-auto text-[13px] leading-5">
+            <CustomScrollbar as="ul" className="max-h-72" viewportClassName="flex flex-col gap-2 text-[13px] leading-5">
               {rest.map((label, index) => (
                 <li key={index} className="flex items-start gap-2 [overflow-wrap:anywhere]">
                   <span aria-hidden className="mt-2 size-1.5 shrink-0 rounded-full bg-(--pn-accent)" />
                   {label}
                 </li>
               ))}
-            </ul>
+            </CustomScrollbar>
           </PopoverContent>
         </Popover>
       )}

src/components/primitives/confirm-dialog.tsx

@@ -2,6 +2,7 @@ import { AlertDialog as AlertDialogPrimitive } from "@base-ui/react/alert-dialog
 import { type LucideIcon, TriangleAlert } from "lucide-react"
 import { type ReactElement, type ReactNode, useRef, useState } from "react"
 
+import { CustomScrollbar } from "@/components/primitives/custom-scrollbar"
 import {
   AlertDialog,
   AlertDialogCancel,
@@ -120,7 +121,7 @@ export function ConfirmDialog({
           finalFocus={finalFocus ? () => finalFocus() ?? true : undefined}
           className={cn(dialogPanel, dialogMotion, "max-w-[460px]")}
         >
-          <div className="flex min-h-0 items-start gap-3.5 overflow-y-auto px-5.5 pt-5 pb-5">
+          <CustomScrollbar className="min-h-0 flex-1" viewportClassName="flex items-start gap-3.5 px-5.5 pt-5 pb-5">
             {Icon ? (
               <span
                 aria-hidden
@@ -138,7 +139,7 @@ export function ConfirmDialog({
               <AlertDialogDescription className={dialogDescriptionText}>{description}</AlertDialogDescription>
               {error && <InlineAlert className="mt-3">{error}</InlineAlert>}
             </div>
-          </div>
+          </CustomScrollbar>
           <div className={dialogFooter}>
             <AlertDialogCancel ref={cancelRef} disabled={pending} className={dialogFooterButton}>
               {cancelLabel}

src/components/primitives/custom-scrollbar.tsx

@@ -0,0 +1,217 @@
+import {
+  type ComponentPropsWithoutRef,
+  type ElementType,
+  type KeyboardEvent,
+  type PointerEvent,
+  type ReactNode,
+  type Ref,
+  useCallback,
+  useEffect,
+  useImperativeHandle,
+  useId,
+  useRef,
+  useState,
+} from "react"
+
+import { cn } from "@/lib/utils"
+
+type ScrollMetrics = {
+  maxScroll: number
+  thumbSize: number
+  thumbOffset: number
+  trackSize: number
+}
+
+type CustomScrollbarProps<E extends ElementType> = {
+  as?: E
+  /** Sizing and layout classes for the outer grid. */
+  className?: string
+  /** Classes for the actual scrollable viewport. */
+  viewportClassName?: string
+  /** Ref to the scrollable element. */
+  scrollRef?: Ref<HTMLElement>
+  /** Accessible label for the scrollbar control. */
+  scrollLabel?: string
+  children?: ReactNode
+} & Omit<ComponentPropsWithoutRef<E>, "as" | "className" | "children" | "ref">
+
+/** A scroll area with a themed, draggable scrollbar instead of the browser's scrollbar. */
+export function CustomScrollbar<E extends ElementType = "div">({
+  as,
+  className,
+  viewportClassName,
+  scrollRef,
+  scrollLabel,
+  children,
+  ...props
+}: CustomScrollbarProps<E>) {
+  // SAFETY: `as` accepts only React element types, and the fallback is a native div.
+  const ScrollElement = (as ?? "div") as ElementType
+  const localScrollRef = useRef<HTMLElement | null>(null)
+  const trackRef = useRef<HTMLDivElement>(null)
+  const dragRef = useRef<{ pointerId: number; startY: number; startScroll: number } | null>(null)
+  const generatedId = useId()
+  const [metrics, setMetrics] = useState<ScrollMetrics>({ maxScroll: 0, thumbSize: 0, thumbOffset: 0, trackSize: 0 })
+  useImperativeHandle(scrollRef, () => {
+    const element = localScrollRef.current
+    if (!element) throw new Error("Custom scrollbar viewport did not mount.")
+    return element
+  }, [scrollRef])
+
+  const measure = useCallback(() => {
+    const element = localScrollRef.current
+    const track = trackRef.current
+    if (!element || !track) return
+
+    const maxScroll = Math.max(0, element.scrollHeight - element.clientHeight)
+    const trackSize = track.clientHeight
+    const thumbSize =
+      maxScroll > 0
+        ? Math.min(trackSize, Math.max(24, (trackSize * element.clientHeight) / element.scrollHeight))
+        : trackSize
+    const thumbOffset = maxScroll > 0 ? ((trackSize - thumbSize) * element.scrollTop) / maxScroll : 0
+    setMetrics((current) =>
+      current.maxScroll === maxScroll &&
+      current.thumbSize === thumbSize &&
+      current.thumbOffset === thumbOffset &&
+      current.trackSize === trackSize
+        ? current
+        : { maxScroll, thumbSize, thumbOffset, trackSize }
+    )
+  }, [])
+
+  useEffect(() => {
+    const element = localScrollRef.current
+    if (!element) return
+
+    let frame = 0
+    const scheduleMeasure = () => {
+      cancelAnimationFrame(frame)
+      frame = requestAnimationFrame(measure)
+    }
+    const resizeObserver = new ResizeObserver(scheduleMeasure)
+    resizeObserver.observe(element)
+    if (element.firstElementChild) resizeObserver.observe(element.firstElementChild)
+    const mutationObserver = new MutationObserver(scheduleMeasure)
+    mutationObserver.observe(element, { childList: true, subtree: true, characterData: true, attributes: true })
+    element.addEventListener("scroll", scheduleMeasure, { passive: true })
+    window.addEventListener("resize", scheduleMeasure)
+    scheduleMeasure()
+
+    return () => {
+      cancelAnimationFrame(frame)
+      resizeObserver.disconnect()
+      mutationObserver.disconnect()
+      element.removeEventListener("scroll", scheduleMeasure)
+      window.removeEventListener("resize", scheduleMeasure)
+    }
+  }, [measure])
+
+  function onTrackPointerDown(event: PointerEvent<HTMLDivElement>) {
+    if (event.target !== event.currentTarget || metrics.maxScroll === 0) return
+    const element = localScrollRef.current
+    if (!element) return
+    const rect = event.currentTarget.getBoundingClientRect()
+    const clickPosition = event.clientY - rect.top
+    const targetPosition = Math.max(0, Math.min(metrics.trackSize, clickPosition - metrics.thumbSize / 2))
+    const travel = Math.max(1, metrics.trackSize - metrics.thumbSize)
+    element.scrollTop = (targetPosition / travel) * metrics.maxScroll
+  }
+
+  function onThumbPointerDown(event: PointerEvent<HTMLDivElement>) {
+    if (metrics.maxScroll === 0) return
+    event.preventDefault()
+    event.stopPropagation()
+    event.currentTarget.setPointerCapture(event.pointerId)
+    dragRef.current = {
+      pointerId: event.pointerId,
+      startY: event.clientY,
+      startScroll: localScrollRef.current?.scrollTop ?? 0,
+    }
+  }
+
+  function onThumbPointerMove(event: PointerEvent<HTMLDivElement>) {
+    const drag = dragRef.current
+    const element = localScrollRef.current
+    if (!drag || drag.pointerId !== event.pointerId || !element) return
+    const travel = Math.max(1, metrics.trackSize - metrics.thumbSize)
+    element.scrollTop = drag.startScroll + ((event.clientY - drag.startY) / travel) * metrics.maxScroll
+  }
+
+  function onThumbPointerEnd(event: PointerEvent<HTMLDivElement>) {
+    if (dragRef.current?.pointerId === event.pointerId) dragRef.current = null
+  }
+
+  function onScrollbarKeyDown(event: KeyboardEvent<HTMLDivElement>) {
+    const element = localScrollRef.current
+    if (!element) return
+    const page = Math.max(40, element.clientHeight * 0.9)
+    const amount = Math.max(24, element.clientHeight * 0.1)
+    let nextPosition: number
+    switch (event.key) {
+      case "ArrowDown":
+        nextPosition = element.scrollTop + amount
+        break
+      case "ArrowUp":
+        nextPosition = element.scrollTop - amount
+        break
+      case "PageDown":
+        nextPosition = element.scrollTop + page
+        break
+      case "PageUp":
+        nextPosition = element.scrollTop - page
+        break
+      case "Home":
+        nextPosition = 0
+        break
+      case "End":
+        nextPosition = metrics.maxScroll
+        break
+      default:
+        return
+    }
+    event.preventDefault()
+    element.scrollTop = nextPosition
+  }
+
+  return (
+    <div className={cn("custom-scroll-area", className)}>
+      <ScrollElement
+        {...props}
+        id={generatedId}
+        ref={localScrollRef}
+        className={cn("custom-scroll-area__viewport", viewportClassName)}
+      >
+        {children}
+      </ScrollElement>
+      <div
+        ref={trackRef}
+        role="scrollbar"
+        aria-label={scrollLabel ?? "Scroll content"}
+        aria-controls={generatedId}
+        aria-orientation="vertical"
+        aria-valuemin={0}
+        aria-valuemax={metrics.maxScroll}
+        aria-valuenow={localScrollRef.current?.scrollTop ?? 0}
+        tabIndex={metrics.maxScroll > 0 ? 0 : -1}
+        onKeyDown={onScrollbarKeyDown}
+        onPointerDown={onTrackPointerDown}
+        className="custom-scroll-area__track"
+        data-visible={metrics.maxScroll > 0 ? "" : undefined}
+      >
+        <div
+          className="custom-scroll-area__thumb"
+          style={{
+            height: `${metrics.thumbSize}px`,
+            transform: `translateY(${metrics.thumbOffset}px)`,
+          }}
+          onPointerDown={onThumbPointerDown}
+          onPointerMove={onThumbPointerMove}
+          onPointerUp={onThumbPointerEnd}
+          onPointerCancel={onThumbPointerEnd}
+          onLostPointerCapture={onThumbPointerEnd}
+        />
+      </div>
+    </div>
+  )
+}

src/components/primitives/form-dialog.tsx

@@ -2,6 +2,7 @@ import { Dialog as DialogPrimitive } from "@base-ui/react/dialog"
 import { type LucideIcon, TriangleAlert, X } from "lucide-react"
 import { type KeyboardEvent, type ReactElement, type ReactNode, useRef, useState } from "react"
 
+import { CustomScrollbar } from "@/components/primitives/custom-scrollbar"
 import { Button } from "@/components/ui/button"
 import {
   Dialog,
@@ -103,7 +104,7 @@ export function FormDialog({
   const [submitError, setSubmitError] = useState<string | null>(null)
   const [confirmingDiscard, setConfirmingDiscard] = useState(false)
   const popupRef = useRef<HTMLDivElement>(null)
-  const bodyRef = useRef<HTMLDivElement>(null)
+  const bodyRef = useRef<HTMLElement>(null)
   const shownError = error ?? submitError
 
   function requestClose() {
@@ -181,9 +182,13 @@ export function FormDialog({
             onKeyDown={onFormKeyDown}
             className="flex min-h-0 flex-1 flex-col"
           >
-            <div ref={bodyRef} className="flex min-h-0 flex-1 flex-col gap-4 overflow-y-auto px-5.5 py-4.5">
+            <CustomScrollbar
+              scrollRef={bodyRef}
+              className="min-h-0 flex-1"
+              viewportClassName="flex flex-col gap-4 px-5.5 py-4.5"
+            >
               {children}
-            </div>
+            </CustomScrollbar>
             {(shownError || notice) && (
               <div className="flex shrink-0 flex-col gap-2 px-5.5 pb-4">
                 {notice}

src/components/primitives/label-tree-selector.tsx

@@ -1,6 +1,7 @@
 import { Check, ChevronRight, Minus, Search, X } from "lucide-react"
 import { useMemo, useState } from "react"
 
+import { CustomScrollbar } from "@/components/primitives/custom-scrollbar"
 import {
   buildLabelTree,
   collectSubtreeLabels,
@@ -204,7 +205,7 @@ export function LabelTreeSelector({
       {selectedLabels.length > 0 && (
         // Own block under the search: two 24px lines (plus the 4px gap) then it scrolls; 8px below the chips.
         <div className="shrink-0 border-b border-(--pn-line) px-2 pt-2 pb-2">
-          <div className="flex max-h-[52px] flex-wrap content-start gap-1 overflow-y-auto">
+          <CustomScrollbar className="max-h-[52px]" viewportClassName="flex max-h-[52px] flex-wrap content-start gap-1">
             {selectedLabels.map((label) => (
               <button
                 key={label.label}
@@ -218,11 +219,11 @@ export function LabelTreeSelector({
                 <X aria-hidden className="size-3 text-(--pn-fg-muted)" />
               </button>
             ))}
-          </div>
+          </CustomScrollbar>
         </div>
       )}
 
-      <div className="min-h-0 flex-1 overflow-y-auto p-1">
+      <CustomScrollbar className="min-h-0 flex-1" viewportClassName="p-1">
         {showTree && (
           <section>
             <SectionTitle>Categories</SectionTitle>
@@ -266,7 +267,7 @@ export function LabelTreeSelector({
             className="px-2 py-6"
           />
         )}
-      </div>
+      </CustomScrollbar>
     </div>
   )
 }