Fluent UI React v9 for Word Add-ins

Quick Start

Wrap the app root with FluentProvider and a theme:

import { FluentProvider, webLightTheme } from '@fluentui/react-components';

Office.onReady(() => {
  createRoot(document.getElementById('container')!).render(
    <FluentProvider theme={webLightTheme}>
      <App />
    </FluentProvider>
  );
});

Core Concepts

Component Architecture

v9 components separate behavior, styling, and rendering into hooks:

const MyComponent = React.forwardRef((props, ref) => {
  const state = useMyComponent(props, ref);  // behavior
  useMyComponentStyles(state);               // styling
  return renderMyComponent(state);           // render
});

This enables recomposition - reassemble hooks to create custom variants without forking.

Styling with Griffel

import { makeStyles, makeResetStyles, mergeClasses, shorthands, tokens } from '@fluentui/react-components';

// Base styles (single monolithic class - use for base/default state)
const useBaseClassName = makeResetStyles({
  display: 'flex',
  padding: '8px 12px',  // CSS shorthands OK in makeResetStyles
  color: tokens.colorNeutralForeground1,
  ':hover': { backgroundColor: tokens.colorNeutralBackground1Hover },
});

// Variant styles (atomic classes - use for conditional overrides)
const useStyles = makeStyles({
  primary: {
    backgroundColor: tokens.colorBrandBackground,
    color: tokens.colorNeutralForegroundOnBrand,
  },
  small: { ...shorthands.padding('4px', '8px') },  // Must use shorthands.* in makeStyles
});

function MyButton({ appearance, size, className }) {
  const base = useBaseClassName();
  const styles = useStyles();
  return (
    <button className={mergeClasses(
      base,
      appearance === 'primary' && styles.primary,
      size === 'small' && styles.small,
      className,  // consumer override always last
    )} />
  );
}

Critical rules:

Never concatenate Griffel classes with +; always use mergeClasses()
Call mergeClasses() once per element, not nested
Use tokens.* for all colors, spacing, typography; never raw values
makeResetStyles allows CSS shorthands; makeStyles requires shorthands.* helpers

Slots

Slots let consumers customize component parts:

// Props to a slot
<Button icon={{ className: styles.icon, 'aria-hidden': true }}>Click</Button>

// JSX element as slot content
<Button icon={<MyIcon />}>Click</Button>

// Disable a slot
<Button icon={null}>No icon</Button>

// Render function (escape hatch - replaces the slot element entirely)
<Button icon={{ children: (Component, props) => <b>!</b> }}>Alert</Button>

Event Handlers

v9 uses the (event, data) convention:

<Input onChange={(ev, data) => console.log(data.value)} />
<Checkbox onChange={(ev, data) => console.log(data.checked)} />
<Dropdown onOptionSelect={(ev, data) => console.log(data.selectedOptions)} />

Reference Files

Consult these for detailed guidance:

v9-component-architecture.md - Complete v9 architecture docs: hooks pattern, slots system, FluentProvider, theming, design tokens, recomposition, custom styling hooks, props conventions, accessibility. Read when building custom components or needing deeper architectural understanding.
griffel-styling.md - Full Griffel API reference: makeStyles, makeResetStyles, mergeClasses, shorthands.*, RTL handling, @noflip, nested selectors, performance rules, tokens usage. Read when styling components or troubleshooting CSS issues.
word-addin-patterns.md - Word add-in specific patterns: task pane layout, responsive design (300-600px), Office theme detection, forms, lists, toolbars, dialogs, message bars, progress states, Office JS API integration, accessibility and focus management. Read when building Word add-in UI.

Key Component Reference

Layout

FluentProvider, Card, Divider, Drawer, TabList/Tab

Input

Button, Input, Textarea, Select, Dropdown/Option, Checkbox, Switch, RadioGroup/Radio, Slider, SpinButton, DatePicker, Combobox

Data Display

Avatar, Badge, Tag, DataGrid, Table, Tree, Accordion, Text, Title*, Subtitle*, Body*, Caption*

Feedback

Spinner, ProgressBar, MessageBar, Toast, Dialog, Popover, Tooltip, Alert

Navigation

Toolbar/ToolbarButton, Menu/MenuItem, Breadcrumb, Link, Nav/NavItem

Icons

Import from @fluentui/react-icons: import { AddRegular, DeleteRegular } from '@fluentui/react-icons'

Icon naming: {Name}{Style} where Style is Regular, Filled, or size variants like 20Regular.

Word Add-in Guidelines

Task Pane Defaults

Width: ~320px (resizable 300-600px); design mobile-first
Use height: 100vh with flex column layout
Scrollable content area with fixed header/footer
Match Office host theme via FluentProvider

Accessibility Requirements

All interactive elements must be keyboard accessible
Use role="status" with aria-live="polite" for operation feedback
Return focus to the task pane after Word API operations
Support high contrast via @media (forced-colors: active) with system colors
Use semantic HTML (<button>, <input>) over styled <div>s

Performance

Define makeStyles/makeResetStyles at module scope, not inside components
Use React.lazy for heavy panels to keep initial load fast
Tree-shake icons with direct imports: import { AddRegular } from '@fluentui/react-icons'
Memoize callbacks that interact with the Word API

fluent-ui-react