Let's perform some troubleshooting steps to get rid of the black background in QuickBooks Online (QBO), steve118.
It's possible the browser's cache data is full or damaged causing the background don't load properly. To better isolate this one, let's try accessing QBO using a private window. This mode doesn't use the existing cache data and helps us confirm browser-related issues.
Just press CTRL + Shift + N for Google Chrome, or click the Settings and More icon in the upper-right hand corner, and then select New In Private window for Microsoft Edge.