Styling in stateless UI components

Keep styles separated from the parts of the app that are tied to state. That means routes, views, containers, forms, layouts, etc. should not have any styling or classes in them. Instead, these heavy-lifting components should be composed of primarily stateless functional UI components.

Form component (with no styles/classNames) - just pure composed components

class SampleComponent extends Component {
  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <Heading children='Sign In'/>
        <Input
          name='username'
          value={username}
          onChange={this.handleChange}/>
        <Input
          type='password'
          name='password'
          value={password}
          onChange={this.handleChange}/>
        <Button
          type='submit'
          children='Sign In'/>
      </form>
    )
  }
}

// Presentational component (with Styles)
const Button = ({
  ...props
  }) => {
  const sx = {
    fontFamily: 'inherit',
    fontSize: 'inherit',
    fontWeight: 'bold',
    textDecoration: 'none',
    display: 'inline-block',
    margin: 0,
    paddingTop: 8,
    paddingBottom: 8,
    paddingLeft: 16,
    paddingRight: 16,
    border: 0,
    color: 'white',
    backgroundColor: 'blue',
    WebkitAppearance: 'none',
    MozAppearance: 'none'
  }

  return (
    <button {...props} style={sx}/>
  )
}