Currently, the new Vector sets a different background color for .skin-vector-max-width, which can give users the impression that something is wrong about the site and browser when viewing in widescreen.
Also, currently, the sidebar also has a background, which feels awkward when the overall page content is too short, which makes the sidebar background ended abruptly in mid-air, removing the background should feel more consistent.
In Old Vector Skin
In Current Vector Skin
Removing background color of .skin-vector-max-width
By removing the background color and the border color, it felt more consistent.