Today I learned that on macOS, with the default scrollbar setting enabled, classic scrollbars are shown automatically when a mouse is connected. I used to believe that, mouse or not, users needed to explicitly change the scrollbar appearance to get the classic scrollbars.
This is relevant for everyone who builds websites because when classic scrollbars are shown, the value of 100vw includes the scrollbar width. This can cause an unexpected horizontal overflow if the layout relies on 100vw for full-width elements. Additionally, they affect media queries, which assume scrollbars don’t exist when evaluating viewport width.
Having said that, these aren’t new issues. Classic scrollbars are shown by default on Windows, where the same behaviours apply.
Further reading: