I use the Courses view a lot to create routes. Because in the Classic site the map will expand along with the browser window I use fullscreen to get the maximum view.
In the Modern GC the Courses view is constrained within an embedded frame (or some such thing) so that no matter how high I make the browser window the map height is constrained and requires a lot of scrolling. Using the elevation sub-window takes up nearly half the map's window.
As I look around other parts of the new site I have seen other examples of this. Making it harder to use the features just to get a new style isn't helpful and I've switched back to the classic view, and will until I get kicked off it. Plus I can still use the Garmin plugin.
