Use CSS/Jquery calc function in React Js

If you need some more specific CSS you need to put it into quotes – react inline styles doc

<div style={{width: 'calc(100% - 276px)'}}></div>

In your exact case

customFormat="hello-div"
divStyle = {width: 'calc(100% - 276px)'}
return (
    <div className={customFormat} style={divStyle}>
      Hello World
    </div>
)

In case you need to overwrite multiple widths (fallbacks) for browser compatibility

divStyle = {width: 'calc(100% - 276px)',
    fallbacks: [
        { width: '-moz-calc(100% - 276px)' },
        { width: '-webkit-calc(100% - 276px)' },
        { width: '-o-calc(100% - 276px)' }
]}