It has actually almost nothing to do with React, it's a part of JSX syntax (which can be used with other libraries, and React can be used without it). The oute

It has actually almost nothing to do with React, it's a part of JSX syntax (which can be used with other libraries, and React can be used without it). The outer curly braces indicate that there's a JS expression inside, and the inner ones are just a part of an object (think JSON). It could look like this if stored in a variable: let styles = { margin: 0, color: "red" }; … <div style={styles}> https://facebook.github.io/react/docs/introducing-jsx.html#embedding-expressions-in-jsx https://facebook.github.io/react/docs/introducing-jsx.html#e... https://facebook.github.io/react/docs/dom-elements.html#style https://facebook.github.io/react/docs/dom-elements.html#styl...