Framed
Below is the About page, unchanged, rendered inside a window frame. It is the same document at the same address, served once and shown twice.
The frame does not move, resize, stack or respond to anything. There is no JavaScript on this page at all. It exists to answer one question before the real interface is designed: what is different about a page when it is inside a window rather than filling the screen?
What this is for
Three things are known to differ, each measured rather than assumed, and each one lands on a decision that has not been made yet.
A link clicked inside the frame spends a browser history entry that the outer page never sees, so Back moves the framed page instead of closing the window. A colour theme set on the outer page does not reach a frame that is already open. And the framed page applies its own small-screen layout based on the width of the frame rather than the width of the screen, so a narrow window shows the phone layout on a desktop.