Automated triage: Browser issue
Thank you for reporting this issue. The bottom notice is a full-width bar with square corners and a thin border along the edges of the page. The browser window's own rounded corners clip that border at the corner. The page has no way to detect or follow the window's corner shape, so this comes from how the window is drawn, not from the forum's styling.
This is an automated assessment. A member of staff may review and update it.