Upgrade StorageLoading icon color error
The "Loading" icon displayed while reading PDFs has a color issue in dark mode, while it appears normal in light mode.
https://s3.amazonaws.com/zotero.org/images/forums/u13050672/thn6d3y9hzptipt4p7h5.png
https://s3.amazonaws.com/zotero.org/images/forums/u13050672/1tidkmanvkbe8f89wepk.png
https://s3.amazonaws.com/zotero.org/images/forums/u13050672/thn6d3y9hzptipt4p7h5.png
https://s3.amazonaws.com/zotero.org/images/forums/u13050672/1tidkmanvkbe8f89wepk.png
