Since rEFLR985dc2b5d569df5ccf2567f18bd5f6fbe60f8658 by @Jdlrobson the mw-fr-watchlist-pending-notice message ("there are unreviewed changes on your watchlist") uses the warningbox class which comes with styling by default.
In rEFLR frontend/modules/ext.flaggedRevs.basic.css:224-230 (at f5d01c4f70b4) we have redundant and deviant styling for this div by class fr-watchlist-pending-notice (more like errorbox).
As the fr-watchlist-pending-notice class seems to be used nowhere else I propose to remove it completely. For users who want to hide the message it is possible to access it by id.