The map window is as wide as your screen
The original draws a 512×480 window into the map — sixteen tiles by fifteen, which on a modern monitor is a keyhole. The magnifier buttons now enlarge the window itself instead of the picture: the game renders into a frame the size of your browser window, one pixel to one pixel, with no scaling and no blur, so you simply see three times more ground. The side panel moves to the right edge, the minimap, the cursor and the scrolling at the screen edge follow it. The rules do not change at all — the engine never had the screen size hard-coded, it reads it out of memory, so it was enough to hand it a bigger frame. The page always opens at the native size; only the magnifiers change it.