React: Do not add units to css custom properties

Do you want to request a feature or report a bug?

bug

What is the current behavior?

<div style={{ '--value': 5 }}></div>

becomes

<div style="--value: 5px;"></div>

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template: https://jsfiddle.net/84v837e9/).

https://codepen.io/TrySound/pen/MojVOp

What is the expected behavior?

Leave values same as they are passed.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

React 15.6.0