Redmine

The tab bar is meant to overflow horizontally. But the list is sized with a hardcoded constant:

#content .tabs ul {
  min-inline-size: 2000px;
  inline-size: 100%;
}

Past 2000px the tabs wrap to a second row.

The core project settings tabs are about 700px wide, so usually stays under the limit. But the limit is reached on instances whose plugins add tabs to the settings pages, project_settings_tabs being a common extension point.

Proposed patch:

-  min-inline-size: 2000px;
-  inline-size: 100%;
+  min-inline-size: 100%;
+  inline-size: max-content;

min-inline-size: 100% keeps the bottom border spanning the full width of the container when there are only a few tabs.
inline-size: max-content sizes the list to its content, so the tabs stay on a single row whatever their number.