Where I work, we're a small dev team of a few full stack developers and a designer. Our designer does the CSS, and the devs the JS. The separation works well enough for us. YMMV.
It seems odd to only allow the "designer" to manipulate properties of elements and not the elements themselves. If they are allowed to modify DOM elements then in the React world, that is manipulating JS. For us the important separation is at the component level, which includes everything that component needs to render and function (HTML, CSS, JS).
We are not using React.