This document discusses different approaches for using CSS in React applications. It begins by outlining some of the issues with plain CSS, including lack of encapsulation and global namespace pollution. It then examines different methodologies for organizing CSS, including OOCSS, BEM, and SUIT CSS. Next, it covers pre/post-processors like Sass, LESS, and PostCSS. The document dives into examples of implementing styles in React using inline styles, CSS modules, Radium, and Styled Components. For each approach, it highlights the syntax and notes advantages and limitations. Finally, it closes with a brief look at emerging technologies that may impact future CSS practices.

1. CSS
IN
React

2. Joe Sei @joesei

3. THE BAD
THE GOOD
AND THE UGLY

4. Familiarity - (CSS Level 1 released 19 years ago)
Optimized Browser parsing and layout
JavaScript DOM API
Inheritance structure - JSON like
Media Queries - size and feature detection
Pseudo Selectors - browser states
Basic math via calc()
CSS3 (THE GOOD)

5. Flat - nested rules not supported
Needs vendor pre xes
No variables, no functions
Some dynamic updates still require JavaScript
CSS3 (THE BAD)

6. Global namespace pollution
Importance, speci city wars, & eventually !important
Nondeterministic, depends on source order
Encapsulation - sharing code across components is scary
Changes & dead code elimination are manual
Missing rules and syntax errors at runtime
CSS3 (THE UGLY)

7. (like ux for CSS)
Object-Oriented CSS (OOCSS)
Scalable and Modular Architecture for CSS (SMACSS)
Block, Element, Modi er (BEM)
ATOMIC CSS
SUIT CSS
METHODOLOGIES

8. (like babel for CSS)
SASS
LESS
Stylus
PostCSS
Autopre xer / cssnext
PRE/POST PROCESSORS

9. a like button
EXAMPLE:

10. HTML
<button class="btn btn‐primary">
Like <span class="badge">9</span>
</button>

11. OR

12. JSX & REACT
const LikeButton = ({ likes }) => {
return (
<button className="btn btn‐primary">
Like <span className="badge">{likes}</span>
</button>
)
}

13. DOM API
1. const LikeButton = ({ likes }) => {
2. return (
3. <button className="btn btn-primary">
4. Like <span className="badge">{likes}</span>
5. </button>
6. )
7. }
8.

14. AND

15. CSS3.btn {
display: inline‐block;
border: 0;
padding: 6px 12px;
}
.btn.btn‐primary {
color: #fff;
background‐color: #f74A27;
}
.btn.btn‐primary:hover {
background‐color: #ff7857;
}
.btn.btn‐primary > .badge {
color: #f74A27;
background‐color: #fff;
}
.btn > .badge {
display: inline‐block;
border‐radius: 10px;
padding: 3px 6px;
}
SASS.btn {
display: inline‐block;
border: 0;
padding: 6px 12px;
&.btn‐primary {
color: $text‐color;
background‐color: $button‐color;
&:hover {
background‐color: $button‐color‐hover;
}
.badge {
color: $button‐color;
background‐color: $text‐color;
}
}
.badge {
display: inline‐block;
border‐radius: 10px;
padding: 3px 6px;
}
}

16. RESULTLike 9

17. NOW LET'S TRY THE SAME
WITH INLINE STYLES
in React

18. JSONconst styles = {
'btn': {
'display': 'inline‐block',
'border': '0',
'padding': '6px 12px'
},
'btn_primary': {
'color': '#fff',
'backgroundColor': '#f74A27'
},
'btn_primary_hover': {
'backgroundColor': '#ff7857'
},
'btn_primary__badge': {
'color': '#f74A27',
'backgroundColor': '#fff'
}
'btn__badge': {
'display': 'inline‐block',
'borderRadius': '10px',
'padding': '3px 6px'
}
}
REACTimport React, { Component } from 'react'
import { styles } from './styles'
export const LikeButton = ({ likes }) => {
return (
<button style={{
...styles.btn,
...styles.btn_primary
}}>
Like
<span
style={{
...styles.btn__badge,
...styles.btn_primary__badge
}}>
{likes}
</span>
</button>
)
}

19. CSS IN JAVASCRIPT
1. const styles = {
2. 'btn': {
3. 'display': 'inline-block',
4. 'border': '0',
5. 'padding': '6px 12px'
6. },
7.
8. 'btn_primary': {
9. 'color': '#fff',
10. 'backgroundColor': '#f74A27'
11. },
12. 'btn_primary_hover': {
13. 'backgroundColor': '#ff7857'

20. 14. },
IN YOUR COMPONENT
1. import React, { Component } from 'react'
2.
3. import { styles } from './styles'
4.
5. export const LikeButton = ({ likes }) => {
6. return (
7. <button style={{
8. ...styles.btn,
9. ...styles.btn_primary
10. }}>
11. Like
12. <span
13. style={{

21. 14. ...styles.btn__badge,
RESULT WITH JSONLike 9

22. No pseudo selectors :hover :before etc.
No media queries @media viewport etc.
No rule nesting
No auto pre xing
No CSS extraction
FOUC
ISSUES WITH USING THE PLAIN
JSON object

23. Radium
react-css-modules
styled-components
aphrodite, jss, cxs, csjs, glamor, so many more
FRAMEWORKS FOR
CSS in JS

24. RADIUMexport const styles = {
btn: {
display: 'inline‐block',
border: '0',
padding: '6px 12px',
btn_primary: {
color: '#fff',
backgroundColor: '#f74A27',
':hover': {
backgroundColor: '#ff7857'
},
badge: {
color: '#f74A27',
backgroundColor: '#fff'
}
}
badge: {
display: 'inline‐block',
borderRadius: '10px',
padding: '3px 6px'
}
}
}
REACTimport React, { Component } from 'react'
import Radium from 'radium'
import { styles } from './styles'
@Radium
class LikeButton extends Component {
render () {
const { likes } = this.props
return (
<button style={[
styles.btn,
styles.btn.btn_primary
]}>
Like <span style={[
styles.btn.badge,
styles.btn.btn_primary.badge
]}>{likes}</span>
</button>
)
}
}
export default LikeButton

25. RADIUM STYLE SYNTAX
1. export const styles = {
2. btn: {
3. display: 'inline-block',
4. border: '0',
5. padding: '6px 12px',
6.
7. btn_primary: {
8. color: '#fff',
9. backgroundColor: '#f74A27',
10.
11. ':hover': {
12. backgroundColor: '#ff7857'
13. },

26. 14.
RADIUM REACT SYNTAX
1. import React, { Component } from 'react'
2. import Radium from 'radium'
3. import { styles } from './styles'
4.
5. @Radium
6. class LikeButton extends Component {
7. render () {
8. const { likes } = this.props
9. return (
10. <button style={[
11. styles.btn,
12. styles.btn.btn_primary
13. ]}>

27. 14. Like <span style={[
Wraps your function or component with @decorators
Creates a class to manage state for :hover :active :focus
Radium.getState(this.state, 'btnPrimary', ':hover')
Style similar child elements with .map()
matchMedia for media queries - IE poly ll, server-side?
Styles are inline, extract into CSS for production?
RADIUM NOTES

28. No globals (with caveats)
Built in dead code elimination, only used components
Presentation logic is in your view, nd and edit
State, constants
Composition, loops, computation
Distribute via import and export
Dynamic styling, app & DOM state e.g. data attributes
Some :pseudo selectors re-implemented in JavaScript
For example :last-child becomes i === arr.length - 1
INLINE STYLES (THE GOOD)

29. No ::after ::before ::selection
Media queries have to use window.matchMedia()
Autopre xing display: -webkit-flex; display: flex;
Animations via @keyframes re-implemented in JS
Highest priority before !important No Speci city Cascading
Performance
Debugging in devtools is a pain
Duplicate markup for similar elements
INLINE STYLES (THE BAD)

30. CSS MODULES

31. Based on Interoperable CSS - loadable, linkable CSS
Works with SASS, PostCSS etc.
Broken CSS = compile error
Using an unde ned CSS Module = no warning
REACT-CSS-MODULES

32. SASS@import "variables.scss";
.btn {
display: inline‐block;
border: 0;
padding: 6px 12px;
&.btn‐primary {
color: $text‐color;
background‐color: $button‐color;
&:hover {
background‐color: $button‐color‐hover;
}
.badge {
color: $button‐color;
background‐color: $text‐color;
}
}
.badge {
display: inline‐block;
border‐radius: 10px;
padding: 3px 6px;
}
}
REACTimport React, { Component } from 'react'
import CSSModules from 'react‐css‐modules'
import styles from '../styles/likebutton.scss'
@CSSModules(styles, {allowMultiple: true})
class LikeButton extends Component {
render () {
const { likes } = this.props
return (
<button styleName="btn btn‐primary">
Like <span styleName="badge">{likes}</span>
</button>
)
}
}
export default LikeButton

33. REACT-CSS-MODULES SYNTAX
1. import React, { Component } from 'react'
2. import CSSModules from 'react-css-modules'
3. import styles from '../styles/likebutton.scss'
4.
5. @CSSModules(styles, {allowMultiple: true})
6. class LikeButton extends Component {
7. render () {
8. const { likes } = this.props
9. return (
10. <button styleName="btn btn-primary">
11. Like <span styleName="badge">{likes}</span>
12. </button>
13. )

34. 14. }
styles object or this.props.styles[yourClasslassName]
Con gure your component classnames via localIdentName
Webpack CSS loader [path]___[name]__[local]___[hash:base64:5]
Generated classname styles-___likebutton__btn-primary___HYx7V
No overruling, intentionally nor unintentionally
Composition composes: parentClass same as @extend in Sass
Others from ICSS :global :export :import
Use extract text plugin in production
REACT-CSS-MODULES NOTES

35. STYLED COMPONENTS

36. STYLEDimport styled from 'styled‐components'
const StyledLikeButton = styled.button`
display: inline‐block;
border: 0;
padding: 6px 12px,
&.btn‐primary {
color: #fff;
background‐color: #f74A27;
&:hover {
background‐color: #ff7857;
}
.badge {
color: #f74A27;
background‐color: ${THEME.bgColor};
}
}
.badge {
display: inline‐block;
border‐radius: 10px;
padding: 3px 6px;
}
`
export default StyledLikeButton
REACTimport React, { Component } from 'react'
import StyledLikeButton from './StyledLikeButton'
class LikeButton extends Component {
render () {
const { likes } = this.props
return (
<StyledLikeButton className="btn‐primary">
Like <span className="badge">{likes}</span>
</StyledLikeButton>
)
}
}
export default LikeButton

37. STYLED COMPONENTS SYNTAX
1. import styled from 'styled-components'
2.
3. const StyledLikeButton = styled.button`
4. display: inline-block;
5. border: 0;
6. padding: 6px 12px,
7. &.btn-primary {
8. color: #fff;
9. background-color: #f74A27;
10. &:hover {
11. background-color: #ff7857;
12. }
13. .badge {

38. 14. color: #f74A27;
STYLED COMPONENTS USAGE
1. import React, { Component } from 'react'
2. import StyledLikeButton from './StyledLikeButton'
3.
4. class LikeButton extends Component {
5.
6. render () {
7. const { likes } = this.props
8. return (
9. <StyledLikeButton className="btn-primary">
10. Like <span className="badge">{likes}</span>
11. </StyledLikeButton>
12. )
13. }

39. 14.
Autopre xing included for free
Write plain CSS, no weird poly lls needed
Generated classnames are namespaced btn-primary gjkSC
Injects style tags into the document head
Supports server-side rendering, but not extract text plugin
keyframes helper keeps your rules local to your component
Theming is built in
STYLED COMPONENTS NOTES

40. Web Components and Shadow DOM
cssnext
CSS4
¿¡ !?
WHAT'S NEXT

41. View examples on Github
THANK YOU!