Remove white banner

As previously mentioned, you could a SPFx Application Customizer to inject css into the page. But, before doing so, what is the ROI for this? I understand it may take up more space than you'd like in your environment, but injecting css to modify code (html) that you don't have control over, adds a layer of technical debt that should likely be avoided. I would question whether it's worth adding this debt, just to remove a few pixels in height on the page. :)