conditional_styling_react_component.css

.Btn {
  padding: .8em 1.5em;
  color: white;
  background-color: #EC87C0;
  border: none;
}

.disabled {
  background-color: #BBBBBB;
}

conditional_styling_react_component.js

import style from './style'
import React from 'react'
import cn from 'classnames'
import CSSModules from 'react-css-modules'

/**
 * Notice use of `styleName` vs. `className`
 */
const Btn = React.createClass({
  render () {
    const { isDisabled } = this.props
    return (
      <button styleName={cn('Btn', {
        disabled: isDisabled
      })}>
        Submit
      <button>
    )
  }
})

export default CSSModules(Btn, style)