I have completed the Technical Documentaion Page project in 8 hours, (from midnight till morning). I did most of checks necessary and added a pure CSS toggle element for sliding of side navigation bar as well. I think everything went well. I did used normalize.css to reduce the inconsistencies in various browsers. Since it was not JS so I thought I could use it.
Can you clarify more? I have tested it on Moto G4 , Galaxy S5, Pixel 2, Pixel 2 XL, iPhone 5 / SE , iPhone 6 / 7 / 8, iPhone 6 / 7 / 8 plus , iPhone X, iPad and iPad pro. In none of the above devices overflow happens. Of course the code is set to collapse the navigation bar on really small screens such as iPhone 5 but it i could be pulled back by the navigation toggle button on the left bottom corner of the screen. Code parts are given horizontal scroll bars since we cannot word wrap code as it will be difficult to read them.