In the header of Hub sites, the first menu item text has an off-center (left-justified) underline, while all the other menu item underlines are centered under the text. I talked to ESRI support about this, and they said it's by design. I'd like to suggest that this is adjusted for a more cohesive look.
I really like that I can add my own HTML and CSS to customize the header in ArcGIS Hub (which I did), but I think that many users might not know how to configure this.