Revert "Now in screen_rect min is the viewport position and max is the viewport size"

This reverts commit 4bbdab1788.

crates/egui_demo_lib/src/lib.rs

@@ -116,6 +116,6 @@ fn test_egui_zero_window_size() {
 /// Detect narrow screens. This is used to show a simpler UI on mobile devices,
 /// especially for the web demo at <https://egui.rs>.
 pub fn is_mobile(ctx: &egui::Context) -> bool {
-    let screen_size = ctx.screen_rect().max;
+    let screen_size = ctx.screen_rect().size();
     screen_size.x < 550.0
 }