react.dev/tips/02-inline-styles.md

id	title	layout	permalink	next	prev
inline-styles	Inline Styles	tips	inline-styles.html	if-else-in-JSX.html	introduction.html

In React, inline styles are not specified as a string. Instead they are specified with an object whose key is the camelCased version of the style name, and whose value is the style's value, usually a string (more on that later):

/** @jsx React.DOM */

var divStyle = {
  color: 'white',
  backgroundImage: 'url(' + imgUrl + ')',
  WebkitTransition: 'all' // note the capital 'W' here
};

React.renderComponent(<div style={divStyle}>Hello World!</div>, mountNode);

Style keys are camelCased in order to be consistent with accessing the properties on DOM nodes from JS (e.g. node.style.backgroundImage). Vendor prefixes should begin with a capital letter. This is why WebkitTransition has an uppercase "W".