I opened it on a phone and redid everything

Today I opened the learning platform on a phone for the first time. The result was grim: the menu did not fit the screen, the buttons were too small for a finger, and the topic list required sideways scrolling. The biggest problem was navigation. A side menu is convenient on a desktop; on a phone it eats half the screen. So I built a bottom bar for phones — a thumb naturally rests at the bottom, and the buttons there are easy to reach. The second problem was going back. On a desktop the browser has a back button and people are used to it. On a phone it feels like moving inside an app, and the user looks for a back button on the screen itself. I added one. That same day another unexpected bug appeared. The database address was being read in two different places in the code, and one of them ignored the environment setting completely. It worked locally, but on the server it connected to the wrong database. Finding it took a while, because the error was not "cannot connect" but "table not found" — the connection succeeded, just to a different database. I tied both places to a single source. The database address is now read from exactly one place. The lesson: testing only on the device you personally use is not enough.