title: How to get the width of a mosaic window?
body: <p>I have some css that needs to change, depending on the size of its containing mosaic window. I'm trying to get the width using <code>onResize</code> but that doesn't appear to be a thing.</p>
  <p>Here's a codesandbox: <a href="https://codesandbox.io/s/react-mosaic-simple-forked-ndjsc8?file=/src/MosaicApp.js" rel="nofollow noreferrer">https://codesandbox.io/s/react-mosaic-simple-forked-ndjsc8?file=/src/MosaicApp.js</a></p>
  <p>Look at line 27 of MosaicApp.js:</p>
  <p><code>onResize={(e)=&gt;alert(JSON.stringify(JSON.parse(e)))}</code></p>