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FloatButton (FAB — Floating Action Button) — spec

Citing Ant Design FloatButton, MUI Fab, shadcn-ui (composition)

Purpose

A round floating button anchored to the screen edge (typically bottom-right). Used for the single most important action on the screen — compose new message, add new item, scroll-to-top.

When FAB vs alternatives

Pattern Use
FAB One primary action, mobile-primary product
Bottom CTA (full-width footer button) Form submit, "Pay" — context-specific
Header action button When the action is contextual to the page header
Inline button in list Per-item actions

A FAB must be the single most important action. Don't use it for navigation. Don't have multiple FABs at the same time.

Anatomy

[viewport]
                                   ┌─────┐
                                   │  +  │   ← FAB
                                   └─────┘
                                   ▼ tap

With expand menu:
                                   ┌────┐
                                   │ 📷 │  ← child action
                                   └────┘
                                   ┌────┐
                                   │ 📝 │
                                   └────┘
                                   ┌─────┐
                                   │  ✕  │  ← rotated FAB (close)
                                   └─────┘
Slot Required Notes
Icon yes Single, recognizable (+, 📝, 📷, ↑)
Label optional "Extended FAB" — text alongside icon
Child actions optional Speed-dial menu when tapped

API

<FloatButton
  icon={<PlusIcon />}
  onClick={openAddModal}
  position="bottom-right"
  label="Add"
/>

// With expand menu (Speed Dial)
<FloatButton.Group icon={<PlusIcon />} position="bottom-right">
  <FloatButton.Item icon={<CameraIcon />} label="사진" onClick={takePhoto} />
  <FloatButton.Item icon={<PenIcon />} label="메모" onClick={addNote} />
  <FloatButton.Item icon={<MicIcon />} label="음성" onClick={recordVoice} />
</FloatButton.Group>
Prop Type Default Description
icon ReactNode — Required
label string — Extended-FAB label
onClick () => void —
position "bottom-right" \| "bottom-left" \| "bottom-center" "bottom-right" Screen-edge anchor
offset [number, number] [16, 16] (mobile) / [24, 24] (desktop) px from edge
size "sm" \| "md" \| "lg" "md"
variant "primary" \| "secondary" \| "tonal" "primary"
disabled boolean false
tooltip string — Optional hover hint (desktop)

Sizes

Size Diameter Icon Use
sm 40px 20px Inline / dense
md (default) 56px 24px Standard mobile FAB
lg 64px 28px Tablet / hero

Material 3's "extended FAB" with label: ~48px height + label text padding.

States

State Visual
Default Resting; raised shadow
Hover Slight scale up + shadow deepen
Pressed Scale 0.96
Focus-visible 2px ring around
Expanded (Speed Dial open) Backdrop dim, child actions visible above, FAB rotates to ✕

Tokens consumed

--color-primary-default       (default FAB bg)
--color-on-primary             (icon)
--color-bg-elevated           (tonal variant)
--color-text-primary
--color-focus-ring
--space-md, --space-base
--radius-full                  (circular)
--radius-lg                    (extended FAB)
--shadow-3                     (elevation when raised)
--shadow-4                     (elevation when expanded)
--motion-fast, --easing-out
--z-fab                        (above content, below modals)

Safe area on mobile

iOS / Android devices have safe-area insets (home bar, notches). FAB position must respect them:

.fab {
  position: fixed;
  bottom: max(16px, calc(16px + env(safe-area-inset-bottom)));
  right: max(16px, calc(16px + env(safe-area-inset-right)));
}

In RN: use useSafeAreaInsets() hook.

Bottom navigation interplay

If your app has a bottom-tab-bar (per knowledge/patterns/mobile-navigation.md), the FAB sits above the tab bar with bottom: tabBarHeight + 16.

For the "center action" tab (elevated tab in middle of tab bar): that's a different pattern — not a FAB, integrated into nav.

Accessibility

  • Render as <button> with aria-label (icon-only).
  • For Speed Dial: parent button has aria-haspopup="menu" aria-expanded. Children are role="menuitem".
  • Focus order: FAB is reachable via Tab.
  • High contrast mode: ensure icon visible against bg color.

Keyboard

  • Tab reaches FAB.
  • Enter / Space activates.
  • For Speed Dial: arrow keys move through children, Esc closes.

Variants

primary (default)

Filled with --color-primary-default, on-primary icon. Highest emphasis.

secondary

Filled with secondary brand or neutral elevated. Use when there's a more important primary CTA elsewhere on the page.

tonal (Material 3)

Subtle bg (--color-primary-subtle-bg), primary icon. Less emphasis but still elevated.

Code example

// Standard FAB — add new
<FloatButton
  icon={<PlusIcon />}
  aria-label="새 거래 추가"
  onClick={openAddTransaction}
/>

// Extended (label visible)
<FloatButton
  icon={<PenIcon />}
  label="작성"
  onClick={openCompose}
/>

// Scroll to top variant
<FloatButton
  icon={<ArrowUpIcon />}
  aria-label="맨 위로"
  onClick={() => window.scrollTo({ top: 0, behavior: "smooth" })}
  hidden={scrollY < 200}     // only show when scrolled
/>

// Speed dial
<FloatButton.Group icon={<PlusIcon />}>
  <FloatButton.Item icon={<CameraIcon />} label="사진 촬영" onClick={takePhoto} />
  <FloatButton.Item icon={<NoteIcon />} label="메모 작성" onClick={addNote} />
  <FloatButton.Item icon={<MicIcon />} label="음성 녹음" onClick={recordVoice} />
</FloatButton.Group>

Don't

  • Don't have multiple FABs visible at once.
  • Don't use FAB for navigation — that's a tab.
  • Don't use for destructive actions — too easy to tap accidentally.
  • Don't use FAB on screens where its action wouldn't make sense (settings page, etc.). Show only where the action is contextual.
  • Don't omit aria-label for icon-only.
  • Don't ignore safe-area-inset on mobile.
  • Don't put FAB so close to bottom-tab-bar that taps overlap.

References

Cross-reference