If under Feature preview you enable New Code Search and Code View (Beta) then pages covered by this feature (such as blob URLs) are displayed in a narrow central column despite this style.

Something sets

max-width: 1280px;

https://github.com/apache/httpd/tree/9605760cff84574a013bf337f6cefae2b4f424f6 is fine but https://github.com/apache/httpd/blob/9605760cff84574a013bf337f6cefae2b4f424f6/CMakeLists.txt is not, for example.